Led display with wavelength conversion layer

ABSTRACT

A display and method of manufacture are described. The display may include a substrate including an array of pixels with each pixel including multiple subpixels, and each subpixel within a pixel is designed for a different color emission spectrum. An array of micro LED device pairs are mounted within each subpixel to provide redundancy. An array of wavelength conversion layers comprising phosphor particles are formed over the array of micro LED device pairs for tunable color emission spectrum.

RELATED APPLICATIONS

This application is a continuation of co-pending U.S. patent applicationSer. No. 14/811,417, filed Jul. 28, 2015, which is a continuation ofU.S. patent application Ser. No. 13/920,912, filed on Jun. 18, 2013, nowU.S. Pat. No. 9,111,464 which is herein incorporated by reference.

BACKGROUND

Field

The present invention relates to micro LED devices. More particularlyembodiments of the present invention relate to methods and structuresfor integrating micro LED devices onto a substrate with tunable coloremission spectrum.

Background Information

Quantum dots are semiconductor nanocrystals that can be tuned to emitlight throughout the visible and infrared spectrum. Due to the smallsize of 1 to 100 nm, more typically 1 to 20 nm, quantum dots displayunique optical properties that are different from those of thecorresponding bulk material. The wavelength, and hence color, of thephoto emission is strongly dependent on the size of a quantum dot. Foran exemplary cadmium selenide (CdSe) quantum dot, light emission can begradually tuned from red for a 5 nm diameter quantum dot, to the violetregion for a 1.5 nm quantum dot. There are generally two types ofschemes for quantum dot (QD) excitation. One uses photo excitation, andthe other uses direct electrical excitation.

One proposed implementation for quantum dots is integration into thebacklighting of a liquid crystal display (LCD) panel. Current whitelight emitting diode (LED) backlight technology for LCD panels utilizesa cerium doped YAG:Ce (yttrium aluminum garnet) down-conversion phosphorlayer over a plurality of blue emitting LED chips. The combination ofblue light from the LED chips and a broad yellow emission from theYAG:Ce phosphor results in a near white light. It has been proposed toreplace the YAG:Ce phosphor with a blend of quantum dots to achieve thewhite backlighting. U.S. Pat. No. 8,294,168 describes arranging aquantum dot sealing package over a package including a row of lightemitting device chips in an edge-type backlight unit light sourcemodule. The light source module is positioned at an edge of the LEDdisplay panel so that it emits light through a side surface of a lightguide plate behind the LED display panel, where the light is reflectedtoward the LCD display panel.

SUMMARY OF THE INVENTION

A display panel with one or more wavelength conversion layers andredundancy scheme are disclosed. In an embodiment a display panelincludes a display substrate including an array of pixels, with eachpixel including multiple subpixels, and each subpixel is designed for adifferent emission spectrum. For example, such a configuration may be ared-green-blue (RGB) pixel, including a subpixel designed for redemission, a subpixel designed for green emission, and a subpixeldesigned for blue emission. An array of micro LED device pairs aremounted within each subpixel to form a redundancy scheme, and an arrayof wavelength conversion layers including phosphor particles are formedover the array of micro LED device pairs. Exemplary phosphor particlesinclude quantum dots and particles that exhibit luminescence due totheir composition that do not qualify as quantum dots. Exemplary microLED devices may have a maximum width of 1 μm-100 μm. The array ofwavelength conversion layers can include multiple groups of wavelengthconversion layers, with each group designed to emit a different coloremission spectrum. The different groups of wavelength conversion layerscan be separated into different subpixels. For example, in an RGB pixelarrangement, the different groups of wavelength conversion layers can bedesigned for red, green, and blue emission and separated into the redemission subpixel, green emission subpixel, and blue emission subpixel,respectively.

In some embodiments a wavelength conversion layer is not formed overevery micro LED device. For example, some micro LED devices can be“naked” and it is not required to convert the emission spectrum of themicro LED device with a wavelength conversion layer. The micro LEDdevices can all have the same color emission spectrum, or the array ofmicro LED devices can include groups of micro LED devices designed toemit different color emission spectra, with the different micro LEDdevice groups separated into different subpixels. Various combinationsof micro LED devices color emission spectra and wavelength conversionlayer spectra are available. For example, a pixel can include a pair of“naked” red micro LED devices in a red subpixel, a green emissionwavelength conversion layer over a blue micro LED device in a greensubpixel, and a “naked” blue micro LED device in a blue subpixel, as anexample for one of several manners of forming an RGB pixel arrangementwith redundancy pairs.

The size and shape of wavelength conversion layers can also be varied.In some embodiments, each wavelength conversion layer is formed overonly a single micro LED device. Each wavelength conversion layer mayalso be formed over both micro LED devices of the redundant pair ofmicro LED devices in a subpixel. Wavelength conversion layers may assumea dome shaped configuration such as hemispherical outer surface, and maybe narrowed or flattened. The wavelength conversion layers can alsoassume an elongated shape, such as elongated dome shaped. Lightdistribution layers may be formed between the corresponding micro LEDdevices and the wavelength conversion layers. In some embodiments thelight distribution layers are in the form of light pipes, and may becharacterized with a lateral length or width that is greater than athickness of the light distribution layer. Each light pipe may span overa single subpixel, or multiple subpixels. For example, each light pipemay span over no more than one subpixel and the micro LED device pairsmounted within the subpixel. For example, each light pipe may span overmore than one subpixel and the micro LED device pairs mounted within themore than one subpixel. Each light pipe may span over all of themultiple subpixels within a corresponding pixel and the micro LED devicepairs mounted within the multiple subpixels of the pixel.

A reflective bank layer may be formed within each subpixel, where eachreflective bank layer is independently addressable from workingcircuitry within the substrate. For example, the display substrate maybe a thin film transistor substrate. A ground line may be formed on orwithin the display substrate. One or more top electrode layers can beformed to electrically connect the array of micro LED device pairs tothe ground line. In an embodiment, a first top electrode layer connectsthe first micro LED device of a pair of micro LED device to the groundline, and a separate top electrode layer connects the second micro LEDdevice of the pair to the ground line. In an embodiment micro LED deviceirregularities are within the array of micro LED device pairs. Exemplaryirregularities can be missing, defective, or contaminated micro LEDdevices, and a passivation layer can be formed over the plurality ofirregularities to electrically insulate them from one or more topelectrode layers, which may be formed directly over the irregularitiesor adjusted so that they are not formed directly over theirregularities. Repair micro LED devices may be formed within thesubpixels corresponding to the plurality of micro LED deviceirregularities.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic top view illustration of an active matrix displaypanel in accordance with an embodiment of the invention.

FIG. 1B is a schematic side-view illustration of the active matrixdisplay panel of FIG. 1A taken along lines X-X and Y-Y prior to thetransfer of a pair of micro LED devices in accordance with an embodimentof the invention.

FIG. 1C is a schematic side-view illustration of the active matrixdisplay panel of FIG. 1A taken along lines X-X and Y-Y after thetransfer of a pair of micro LED devices in accordance with an embodimentof the invention.

FIG. 1D is a schematic side-view illustration of an active matrixdisplay panel similar to FIG. 1A taken along lines X-X and Y-Y after thetransfer of a pair of micro LED devices in accordance with an embodimentof the invention.

FIGS. 2A-2D are isometric view illustrations of an arrangement of microLED devices mounted within a reflective bank layer of a subpixel inaccordance with embodiments of the invention.

FIGS. 3A-3C are isometric view illustrations of an arrangement of microLED devices mounted within a reflective bank layer of a subpixel withseparate wavelength conversion layers formed over individual micro LEDdevices in accordance with embodiments of the invention.

FIGS. 4A-4C are isometric view illustrations of an arrangement of microLED devices mounted within a reflective bank layer of a subpixel with asingle wavelength conversion layer formed over the micro LED devices inaccordance with embodiments of the invention.

FIG. 5 is an isometric view illustration of an arrangement of micro LEDdevices mounted within a reflective bank layer of a subpixel with asingle wavelength conversion layer formed over the reflective bankstructure and micro LED devices in accordance with embodiments of theinvention.

FIGS. 6A-6C are isometric view illustrations of an arrangement of microLED devices mounted within a reflective bank layer of a subpixel with anelongated dome shaped wavelength conversion layer formed over the microLED devices in accordance with embodiments of the invention.

FIG. 7A is an isometric view illustration of an arrangement of micro LEDdevices mounted within a reflective bank layer of a subpixel with asingle elongated dome shaped wavelength conversion layer formed over themicro LED devices in accordance with embodiments of the invention.

FIG. 7B is an isometric view illustration of an arrangement of micro LEDdevices mounted within a reflective bank layer of a subpixel with asingle elongated dome shaped wavelength conversion layer formed over thereflective bank structure and micro LED devices in accordance withembodiments of the invention.

FIG. 8A is an isometric view illustration of a pixel including anelongated dome shaped wavelength conversion layer formed over multiplesubpixels in accordance with an embodiment of the invention.

FIG. 8B is an isometric view illustration of a pixel including both anelongated dome shaped wavelength conversion layer formed over multiplesubpixels and an elongated dome shaped wavelength conversion layerformed over a single subpixel in accordance with an embodiment of theinvention.

FIG. 9A is a combination view illustration of a light pipe around aplurality of micro LED devices and a wavelength conversion layer overthe light pipe in accordance with an embodiment of the invention.

FIG. 9B is a cross-sectional side view illustration of a light pipearound a pair of micro LED devices and a wavelength conversion layerover the light pipe in accordance with an embodiment of the invention.

FIGS. 9C-9D are cross-sectional side view illustrations of a taperedlight pipe around a pair of micro LED devices and a wavelengthconversion layer over the tapered light pipe in accordance withembodiments of the invention.

FIG. 10A is a combination view illustration of a light pipe around apair of micro LED devices and a pair of reflective layers over the pairof micro LED devices in accordance with an embodiment of the invention.

FIG. 10B is a cross-sectional side view illustration of a pair ofreflective layers over a wavelength conversion layer and light pipe inaccordance with an embodiment of the invention.

FIG. 10C is a cross-sectional side view illustration of a pair ofreflective layers over a light pipe and underneath a wavelengthconversion layer in accordance with an embodiment of the invention.

FIG. 10D is a combination view illustration of a light pipe around apair of micro LED devices and a pair of reflective layers over the pairof micro LED devices in accordance with an embodiment of the invention.

FIG. 10E is a cross-sectional side view illustration of a pair ofreflective layers over a wavelength conversion layer and light pipe inaccordance with an embodiment of the invention.

FIG. 10F is a cross-sectional side view illustration of a pair ofreflective layers over a light pipe and underneath a wavelengthconversion layer in accordance with an embodiment of the invention.

FIG. 11A is a combination view illustration of a display including aplurality of micro LED devices and a plurality of light pipes andwavelength conversion layers over the plurality of micro LED devices inaccordance with an embodiment of the invention.

FIG. 11B-11E are schematic side view illustrations of pixels inaccordance with an embodiments of the invention.

FIG. 11F is a combination view illustration of a display including aplurality of micro LED devices and a plurality of light pipes andwavelength conversion layers around the plurality of micro LED devicesin accordance with an embodiment of the invention.

FIG. 11G-J are schematic side view illustrations of pixels in accordancewith embodiments of the invention.

FIG. 12A is a cross-sectional side view illustration of a light pipe andwavelength conversion layer over a reflective bank structure inaccordance with an embodiment of the invention.

FIG. 12B is a cross-sectional side view illustration orthogonal to thecross-sectional side view illustration in FIG. 12A illustrating a topelectrode layer formed over a pair of micro LED devices in accordancewith an embodiment of the invention.

FIG. 12C is a cross-sectional side view illustration orthogonal to thecross-sectional side view illustration in FIG. 12A illustrating one ormore top electrode layers formed over a pair of micro LED devices inaccordance with an embodiment of the invention.

FIG. 12D is a cross-sectional side view illustration orthogonal to thecross-sectional side view illustration in FIG. 12A illustrating a topelectrode layer formed over a plurality of micro LED devices inaccordance with an embodiment of the invention.

FIG. 12E is a cross-sectional side view illustration orthogonal to thecross-sectional side view illustration in FIG. 12A illustrating one ormore top electrode layers formed over a pair of micro LED devices inaccordance with an embodiment of the invention.

FIG. 12F is a cross-sectional side view illustration of a plurality ofmicro LED devices with top and bottom contacts within a plurality ofreflective bank structures, and a light pipe and wavelength conversionlayer over the plurality of micro LED devices in accordance with anembodiment of the invention.

FIGS. 13A-13B are cross-sectional side view illustrations of a pluralityof micro LED devices with bottom contacts within a reflective bankstructure, and a light pipe and wavelength conversion layer over theplurality of micro LED devices in accordance with embodiments of theinvention.

FIG. 13C is a cross-sectional side view illustration of a plurality ofmicro LED devices with bottom contacts within a plurality of reflectivebank structures, and a light pipe and wavelength conversion layer overthe plurality of micro LED devices in accordance with an embodiment ofthe invention.

FIG. 14A is an illustration of a single side manner for applyingwavelength conversion layers over micro LED devices, and a black matrixbetween subpixels in accordance with an embodiment of the invention.

FIG. 14B is an illustration of a top press down manner for applyingwavelength conversion layer over micro LED devices, and a black matrixbetween subpixels in accordance with an embodiment of the invention.

FIG. 15 is a top schematic view illustration of a top electrode layerformed over an array of micro LED devices including a variety ofconfigurations in accordance with an embodiment of the invention.

FIG. 16 is a top schematic view illustration of a plurality of separatetop electrode layers formed over an array of micro LED devices includinga variety of configurations in accordance with an embodiment of theinvention.

FIG. 17 is a top schematic view illustration of a plurality of separatetop electrode layers formed over an array of micro LED devices includinga variety of configurations in accordance with an embodiment of theinvention.

FIG. 18 is a top schematic view illustration of a scribed top electrodelayer in accordance with an embodiment of the invention.

FIG. 19 is a top schematic view illustration of a scribed bottom contactlayer in accordance with an embodiment of the invention.

FIG. 20 is a top view schematic illustration of a smart pixel displayincluding a redundancy and repair site configuration in accordance withan embodiment of the invention.

FIG. 21 is a schematic illustration of a display system in accordancewith an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention describe a display in which adisplay substrate includes an array of pixels, with each pixel includingmultiple subpixels, and each subpixel within a pixel is designed for adifferent color emission spectrum. The display includes an array ofmicro LED device pairs, with a pair of micro LED devices being mountedwithin each subpixel. An array of wavelength conversion layerscomprising phosphor particles are formed over the array of micro LEDdevice pairs. In an embodiment, the wavelength conversion layer includesa polymer or glass matrix and a dispersion of phosphor particles (e.g.quantum dots that exhibit luminescence due to their size, and particlesthat exhibit luminescence due to their composition) within the matrix.In this manner, the light emission can be accurately tuned to specificcolors in the color spectrum, with improved color gamut. In addition,the incorporation of micro LED devices in accordance with embodiments ofthe invention can be used to combine the performance, efficiency, andreliability of wafer-based LED devices with the high yield, low cost,mixed materials of thin film electronics, for both lighting and displayapplications. Exemplary micro LED devices which may be utilized withsome embodiments of the invention are described in U.S. Pat. No.8,426,227, U.S. Publication No. 2013/0126081, U.S. patent applicationSer. No. 13/458,932, U.S. patent application Ser. No. 13/711,554, andU.S. patent application Ser. No. 13/749,647 all of which areincorporated herein by reference. The micro LED devices are highlyefficient at light emission and consume very little power (e.g., 250 mWfor a 10 inch diagonal display) compared to 5-10 watts for a 10 inchdiagonal LCD or OLED display, enabling reduction of power consumption ofan exemplary display panel incorporating the micro LED devices andwavelength conversion layers.

In one aspect, embodiments of the invention provide for configurationsthat allow phosphor particles of different emission spectra to beseparated from one another while still providing good color mixing ofthe light as perceived by the viewer. Separating the phosphor particlesfrom each other in each subpixel can prevent secondary absorption oflight emitted from a phosphor particle emitting a different spectrum(e.g. absorption of green light emitted from a green emitting phosphorparticle by a red emitting phosphor particle). This may increaseefficiency and reduce unintended color shift. In the micro LED devicesystems in accordance with embodiments of the invention the spatialcolor separation between different color emitting areas (e.g. subpixels)can be small enough (e.g. approximately 100 μm or less) that it will notbe perceived by the human eye. In this manner, the “micro” LED devicescale enables the arrangement of micro LED devices, light distributionlayers, and wavelength conversion layers including phosphor particleswith small enough pitch (e.g. approximately 100 μm or less) betweenadjacent micro LED devices or subpixels that the spatial colorseparation is not perceived by the human eye. In such a configuration,spatially non-uniform color of the light source often associated withnon-micro LED device systems can be avoided.

In another aspect, embodiments of the invention describe a lightdistribution layer formed over one or more micro LED devices that allowsthe light emitted from a micro LED device to spread out prior toentering the wavelength conversion layer, and also decrease the opticalintensity of light entering the wavelength conversion layer (and colorfilter). The spread out light may result in more even emission from thewavelength conversion layer to be formed over the transparent lightdistribution layer. Consequently reduction of the optical density mayreduce thermal degradation of the phosphor particles in wavelengthconversion layer, prolonging lifetime of the light emitting device. Thismay also increase the chances of color conversion by the phosphorparticles in the wavelength conversion layer without having to increasethe volume loading of the phosphor particles in the wavelengthconversion layer. Spreading out of the light and reduction of theoptical intensity may also reduce the amount of back reflection andemission from the wavelength conversion layer that is absorbed by amicro LED device. In accordance with embodiments of the invention,inclusion of the light distribution layer may increase total lightemission, increase emission uniformity, and increase sharpness of thecolor spectrum for the display.

In another aspect, embodiments of the invention describe light pipeconfigurations that can increase the fill factor for micro LED devices,pixels, or subpixels including micro LED devices. Wafer-based LEDdevices can be characterized as point sources, where light emissionoccupies a small area and has a concentrated output. If wafer-based LEDdevices are secured far enough apart that they can be perceived by thehuman eye (e.g. approximately 100 μm or more) it may be possible thatthe light emitted from the individual LED devices is perceived as smalldots. The light pipe configurations described in accordance withembodiments of the invention can be used to increase the fill factor formicro LED devices, pixels, or subpixels including micro LED devices, sothat the individual micro LED devices are not distinguishable by thehuman eye, and small dots are not perceived.

In another aspect, embodiments of the invention describe a redundancyscheme in which a plurality of bonding sites are available for bonding aplurality of micro LED devices within each subpixel, for example, withineach bank opening for a subpixel. In an embodiment, the redundancyscheme includes bonding layers (e.g. indium posts) at a pair of bondingsites (or more) within a bank opening, with each bonding layer designedto receive a separate micro LED device. In an embodiment, the redundancyscheme can also include a repair bonding site within the bank openingthat is large enough to receive a micro LED device. The repair bondingsite may also optionally include a bonding layer. In this manner, in anembodiment, each bank opening may correspond to a single emission colorof a subpixel, and receives a plurality of micro LED devices of theemission color. If one of the micro LED devices of a pair of micro LEDdevices mounted within a subpixel is defective, then the other micro LEDdevice compensates for the defective micro LED device. In addition, therepair bonding site may be used to bond an additional micro LED deviceif desired. In one embodiment, a redundancy and repair configuration isintegrated into a backplane structure which can improve emissionuniformity across the display panel without having to alter theunderlying thin film transistor (TFT) architecture already incorporatedin conventional active matrix organic light emitting diode (AMOLED)displays. Thus, embodiments of the invention may be compatible withconventional TFT backplane technology of AMOLED displays where the microLED devices replace the organic emission layers of AMOLED displaytechnology.

In various embodiments, description is made with reference to figures.However, certain embodiments may be practiced without one or more ofthese specific details, or in combination with other known methods andconfigurations. In the following description, numerous specific detailsare set forth, such as specific configurations, dimensions andprocesses, etc., in order to provide a thorough understanding of thepresent invention. In other instances, well-known semiconductorprocesses and manufacturing techniques have not been described inparticular detail in order to not unnecessarily obscure the presentinvention. Reference throughout this specification to “one embodiment”means that a particular feature, structure, configuration, orcharacteristic described in connection with the embodiment is includedin at least one embodiment of the invention. Thus, the appearances ofthe phrase “in one embodiment” in various places throughout thisspecification are not necessarily referring to the same embodiment ofthe invention. Furthermore, the particular features, structures,configurations, or characteristics may be combined in any suitablemanner in one or more embodiments.

The terms “spanning”, “over”, “to”, “between” and “on” as used hereinmay refer to a relative position of one layer with respect to otherlayers. One layer “spanning”, “over”, or “on” another layer or bonded“to” another layer may be directly in contact with the other layer ormay have one or more intervening layers. One layer “between” layers maybe directly in contact with the layers or may have one or moreintervening layers.

Referring now to FIGS. 1A-1D schematic top and side-view illustrationsare provided of an active matrix display panel in accordance with anembodiment of the invention. In such an embodiment, the underlying TFTsubstrate 102 can be similar to those in a typical AMOLED backplaneincluding working circuitry (e.g. T1, T2). Referring to FIG. 1A, panel100 may generally include a pixel area 104 including pixels 106 andsubpixels 108 arranged in a matrix, and working circuitry connected toeach subpixel for driving and switching the subpixels. The non-pixelarea generally includes a data driver circuit 109 connected to a dataline of each subpixel to enable data signals (Vdata) to be transmittedto the subpixels, a scan driver circuit 112 connected to scan lines ofthe subpixels to enable scan signals (Vscan) to be transmitted to thesubpixels, a power supply line 114 to transmit a power signal (Vdd) tothe TFTs, and a ground ring 116 to transmit a ground signal (Vss) to thearray of subpixels. As shown, the data driver circuit, scan drivercircuit, power supply line, and ground ring are all connected to aflexible circuit board (FCB) 113 which includes a power source forsupplying power to the power supply line 114 and a power source groundline electrically connected to the ground ring 116. In accordance withembodiments of the invention, each of the subpixels 108 may beindividually addressed with the corresponding underlying TFT circuitrywhile a uniform ground signal is supplied to the top of the pixel area104.

Referring now to FIGS. 1B-1D, openings 131 may be formed in theplanarization layer 122 to contact the working circuitry. Exemplaryplanarization materials include benzocyclobutene (BCB) and acrylic. Theworking circuitry can include traditional 2T1C (two transistors, onecapacitor) circuits including a switching transistor, a drivingtransistor, and a storage capacitor. It is to be appreciated that the2T1C circuitry is meant to be exemplary, and that other types ofcircuitry or modifications of the traditional 2T1C circuitry arecontemplated in accordance with embodiments of the invention. Forexample, more complicated circuits can be used to compensate for processvariations of the driver transistor and the micro LED devices, or fortheir instabilities. Furthermore, while embodiments of the invention aredescribed and illustrated with regard to top gate transistor structuresin the TFT substrate 102, embodiments of the invention also contemplatethe use of bottom gate transistor structures. Likewise, whileembodiments of the invention are described and illustrated with regardto a top emission structure, embodiments of the invention alsocontemplate the use of bottom, or both top and bottom emissionstructures. In addition, embodiments of the invention are described andillustrated below specifically with regard to a high side driveconfiguration including ground tie lines and ground ring. In a high sidedrive configuration a LED may be on the drain side of a PMOS drivertransistor or a source side of an NMOS driver transistor so that thecircuit is pushing current through the p-terminal of the LED.Embodiments of the invention are not so limited may also be practicedwith a low side drive configuration in which case the ground tie linesand ground ring become the power line in the panel and current is pulledthrough the n-terminal of the LED.

A patterned bank layer 126 including bank openings 128 is formed overthe planarization layer 122. Bank layer 126 may be formed by a varietyof techniques such as ink jet printing, screen printing, lamination,spin coating, CVD, and PVD. Bank layer 126 may be opaque, transparent,or semi-transparent to the visible wavelength. Bank layer 126 may beformed of a variety of insulating materials such as, but not limited to,photo-definable acrylic, photoresist, silicon oxide (SiO₂), siliconnitride (SiN_(x)), poly(methyl methacrylate) (PMMA), benzocyclobutene(BCB), polyimide, acrylate, epoxy, and polyester. In an embodiment, banklayer is formed of an opaque material such as a black matrix material.Exemplary insulating black matrix materials include organic resins,glass pastes, and resins or pastes including a black pigment, metallicparticles such as nickel, aluminum, molybdenum, and alloys thereof,metal oxide particles (e.g. chromium oxide), or metal nitride particles(e.g. chromium nitride).

In accordance with embodiments of the invention, the thickness of thebank layer 126 and width of the bank openings 128 described with regardto the following figures may depend upon the height of the micro LEDdevices to be mounted within the opening, height of the transfer headstransferring the micro LED devices, and resolution of the display panel.In an embodiment, the resolution, pixel density, and subpixel density ofthe display panel may account for the width of the bank openings 128.For an exemplary 55 inch television with a 40 PPI (pixels per inch) and211 μm subpixel pitch, the width of the bank openings 128 may beanywhere from a few microns to 206 μm to account for an exemplary 5 μmwide surrounding bank structure between bank openings 128. For anexemplary display panel with 440 PPI and a 19 μm subpixel pitch, thewidth of the bank openings 128 may be anywhere from a few microns to 14μm to account for an exemplary 5 μm wide surrounding bank structure.Width of the bank structure (i.e. between bank openings 128) may be anysuitable size, so long as the structure supports the required processesand is scalable to the required PPI.

Table 1 provides a list of exemplary implementations in accordance withembodiments of the invention for various red-green-blue (RGB) displayswith 1920×1080 p and 2560×1600 resolutions. In the exemplaryembodiments, the 40 PPI pixel density may correspond to a 55 inch1920×1080 p resolution television, and the 326 and 440 PPI pixel densitymay correspond to a handheld device with RETINA (RTM) display. It is tobe appreciated that embodiments of the invention are not limited to RGBcolor schemes or the 1920×1080 p or 2560×1600 resolutions, and that thespecific resolution and RGB color scheme is for illustrational purposesonly.

TABLE 1 Pixel Sub-Pixel Pixels Display Pitch pitch per inch Substrate(x, y) (x, y) (PPI) Possible transfer head array pitch 55″ (634 μm, (211μm, 40 X: Multiples or fractions of 211 μm 1920 × 1080 634 μm) 634 μm)Y: Multiples or fractions of 634 μm 10″ (85 μm, (28 μm, 299 X: Multiplesor fractions of 28 μm 2560 × 1600 85 μm) 85 μm) Y: Multiples orfractions of 85 μm  4″ (78 μm, (26 μm, 326 X: Multiples or fractions of26 μm  640 × 1136 78 μm) 78 μm) Y: Multiples or fractions of 78 μm  5″(58 μm, (19 μm, 440 X: Multiples or fractions of 19 μm 1920 × 1080 58μm) 58 μm) Y: Multiples or fractions of 58 μm

In accordance with embodiments of the invention, the thickness of thebank layer 126 is not too thick in order for the bank structure tofunction. Thickness may be determined by the micro LED device height anda predetermined viewing angle. For example, where sidewalls of the bankopenings 128 make an angle with the planarization layer 122, shallowerangles may correlate to a wider viewing angle of the system. In anembodiment, exemplary thicknesses of the bank layer 126 may be between 1μm-50 μm. In an embodiment the thickness of the bank layer 126 is within5 μm of the thickness of the micro LED devices 400.

A patterned conductive layer is then formed over the patterned banklayer 126. In one embodiment the patterned conductive layer includesreflective bank layer 142 formed within the bank openings 128 and inelectrical contact with the working circuitry. For example, a reflectivebank layer 142 can be formed for each subpixel, wherein each reflectivebank layer functions as a bottom electrode and is independentlyaddressable from working circuitry within the substrate. Accordingly,all micro LED devices that are bonded to one reflective bank layer of asubpixel are addressed together. The patterned conductive layer may alsooptionally include the ground tie lines 144 and/or the ground ring 116.As used herein the term ground “ring” does not require a circularpattern, or a pattern that completely surrounds an object. In addition,while the following embodiments are described and illustrated withregard to a ground line in the form of a ground ring 116 at leastpartially surrounding the pixel area on three sides, it is to beappreciated that embodiments of the invention can also be practiced witha ground line running along one side (e.g. left, right, bottom, top), ortwo sides (a combination of two of the left, right, bottom, top) of thepixel area. Accordingly, it is to be appreciated that in the followingdescription the reference to and illustration of a ground ring, couldpotentially be replaced with a ground line where system requirementspermit.

The patterned conductive layer may be formed of a number of conductiveand reflective materials, and may include more than one layer. In anembodiment, a patterned conductive layer comprises a metallic film suchas aluminum, molybdenum, titanium, titanium-tungsten, silver, or gold,or alloys thereof. In application, the patterned conductive layer mayinclude a stack of layers or metallic films. The patterned conductivelayer may include a conductive material such as amorphous silicon,transparent conductive oxides (TCO) such as indium-tin-oxide (ITO) andindium-zinc-oxide (IZO), carbon nanotube film, or a transparentconducting polymer such as poly(3,4-ethylenedioxythiophene) (PEDOT),polyaniline, polyacetylene, polypyrrole, and polythiophene. In anembodiment, the patterned conductive layer includes a stack of aconductive material and a reflective conductive material. In anembodiment, the patterned conductive layer includes a 3-layer stackincluding top and bottom layers and a reflective middle layer whereinone or both of the top and bottom layers are transparent. In anembodiment, the patterned conductive layer includes a conductiveoxide-reflective metal-conductive oxide 3-layer stack. The conductiveoxide layers may be transparent. For example, the patterned conductivelayer may include an ITO-silver-ITO layer stack. In such aconfiguration, the top and bottom ITO layers may prevent diffusionand/or oxidation of the reflective metal (silver) layer. In anembodiment, the patterned conductive layer includes a Ti—Al—Ti stack, ora Mo—Al—Mo-ITO stack. In an embodiment, the patterned conductive layerincludes an ITO-Ti—Al—Ti-ITO stack. In an embodiment, the patternedconductive layer is 1 μm or less in thickness. The patterned conductivelayer may be deposited using a suitable technique such as, but notlimited to, PVD.

Following the formation of reflective bank layers 142, ground tie lines144, and ground ring 116, an insulator layer 146 may then optionally beformed over the TFT substrate 102 covering the sidewalls of the patteredconductive layer. The insulator layer 146 may at least partially coverthe bank layer 126 and the reflective bank layer 142, ground tie lines144, and/or ground ring 116. In the embodiment illustrated the insulatorlayer 146 completely covers the ground ring 116, however, this isoptional.

In an embodiment, the insulator layer 146 is formed by blanketdeposition using a suitable technique such as lamination, spin coating,CVD, and PVD, and then patterned using a suitable technique such aslithography to form openings exposing the reflective bank layers 142 andopenings 149 exposing the ground tie lines 144. In an embodiment, inkjet printing or screen printing may be used to form the insulator layer146 and openings in the insulator layer without requiring lithography.Insulator layer 146 may be formed of a variety of materials such as, butnot limited to, SiO₂, SiN_(x), PMMA, BCB, polyimide, acrylate, epoxy,and polyester. For example, the insulator layer 146 may be 0.5 μm thick.The insulator layer 146 may be transparent or semi-transparent whereformed over the sidewalls of the reflective bank layers 142 within thebank openings 128 as to not significantly degrade light emissionextraction of the completed system. Thickness of the insulator layer 146may also be controlled to increase light extraction efficiency, and alsoto not interfere with the array of transfer heads during transfer of thearray of light emitting devices to the reflective bank structure. Aswill become more apparent in the following description, the patternedinsulator layer 146 is optional, and represents one manner forelectrically separating conductive layers.

In the embodiment illustrated in FIG. 1B-1C, the reflective bank layers142, ground tie lines 144, and ground ring 116 can be formed of the sameconductive layer. In another embodiment, the ground tie lines 144 and/orground ring 116 can be formed of a conductive material different fromthe reflective bank layer 142. For example, ground tie lines 144 andground ring 116 may be formed with a material having a higherconductivity than the reflective bank layer 142. In another embodiment,ground tie lines 144 and/or ground ring 116 can also be formed withindifferent layers from the reflective bank layers. The ground tie lines144 and ground ring 116 can also be formed within or below the patternedbank layer 126. For example, openings may be formed through thepatterned bank layer 126 when forming the ground tie lines 144 andground ring 116. Openings may also be formed through the patterned banklayer 126 and planarization layer 122 to contact the ground tie lines144. In an embodiment, the ground ring and ground tie lines 144 may havebeen formed during formation of the working circuitry of the TFTsubstrate 102. Accordingly, it is to be appreciated that a number ofpossibilities exist for forming the ground tie lines 144 and ground ring116.

Referring to the embodiment illustrated in FIG. 1B, a plurality ofbonding layers 140 may be formed on the reflective bank layer 142 tofacilitate bonding of micro LED devices. In the specific embodimentillustrated two bonding layers 140 are illustrated for bonding a pair ofmicro LED devices. In an embodiment, the bonding layer 140 is selectedfor its ability to be inter-diffused with a bonding layer on the microLED device (yet to be placed) through bonding mechanisms such aseutectic alloy bonding, transient liquid phase bonding, or solid statediffusion bonding as described in U.S. patent application Ser. No.13/749,647. In an embodiment, the bonding layer 140 has a meltingtemperature of 250° C. or lower. For example, the bonding layer 140 mayinclude a solder material such as tin (232° C.) or indium (156.7° C.),or alloys thereof. Bonding layer 140 may also be in the shape of a post,having a height greater than width. In accordance with some embodimentsof the invention, taller bonding layers 140 may provide an additionaldegree of freedom for system component leveling, such as planarity ofthe array of micro LED devices with the TFT substrate during the microLED device transfer operation and for variations in height of the microLED devices, due to the change in height of the liquefied bonding layersas they spread out over the surface during bonding, such as duringeutectic alloy bonding and transient liquid phase bonding. The width ofthe bonding layers 140 may be less than a width of a bottom surface ofthe micro LED devices to prevent wicking of the bonding layers 140around the sidewalls of the micro LED devices and shorting the quantumwell structures.

FIG. 1C is a schematic side-view illustration of the active matrixdisplay panel of FIG. 1A taken along lines X-X and Y-Y after thetransfer of a pair of micro LED devices 400 in accordance with anembodiment of the invention. The micro LED devices 400 can betransferred and bonded to the substrate 102 as part of an array of microLED devices 400 using a variety of techniques including a transferbonding process, transfer using elastomeric stamps, or transfer andbonding using an electrostatic transfer head array, as described in anyof U.S. Pat. No. 8,333,860, U.S. Pat. No. 8,349,116, U.S. Pat. No.8,415,771, U.S. Pat. No. 8,415,767, or U.S. Pat. No. 8,415,768. In thefollowing embodiments, description is made with regard to a specificvertical micro LED device 400 structures. It is to be appreciated, thatthe specific micro LED devices 400 illustrated is exemplary and thatembodiments of the invention are not limited. For example, embodimentsof the invention may also be practiced with LED devices that are notvertical LED devices. In the particular embodiment illustrated, themicro LED devices 400 include a micro p-n diode between a bottom contact404 and top contact 402. In an embodiment, the micro p-n diode isseveral microns thick, such as 30 μm or less, or even 5 μm or less, withthe top and bottom contacts 404, 402 being 0.1 μm-2 μm thick. The microp-n diode may include a n-doped layer 409, a p-doped layer 405, and oneor more quantum well layers 416 between the n-doped layer and p-dopedlayer. In the particular embodiment illustrated in FIG. 1C the n-dopedlayer 409 is illustrated as being above the p-doped layer 405.Alternatively, the p-doped layer 405 may be above the n-doped layer 409.The micro LED devices 400 may have straight or tapered sidewalls 406(from top to bottom). The top and bottom contacts 402, 404 may includeone or more layers and can be formed of a variety of electricallyconducting materials including metals, conductive oxides, and conductivepolymers. The top and bottom contacts 402, 404 may be transparent orsemi-transparent to the visible wavelength spectrum (e.g. 380 nm-750 nm)or opaque. The top and bottom contacts 402, 404 may optionally include areflective layer, such as a silver layer. In an embodiment, a conformaldielectric barrier layer 407 may optionally be formed along thesidewalls 406 of the p-n diode to electrically passivate the quantumwell 416, and optionally along the top or bottom surface of the microp-n diode. The conformal dielectric barrier layer 407 may be thinnerthan the p-n diode so that it forms an outline of the topography of thep-n diode it is formed on. For example, the conformal dielectric barrierlayer 407 may be approximately 50-600 angstroms thick aluminum oxide. Abonding layer 414 may be positioned between the micro LED device 400 andthe reflective bank layer 142 to facilitate bonding of the bottomcontact 404 of micro LED device 400 to the reflective bank layer 142, orother intervening layer. In an embodiment, bonding layer 414 includes amaterial such as indium, gold, silver, molybdenum, tin, aluminum,silicon, or an alloy or alloys thereof. Bonding layer 414 may be analloy or intermetallic compound of a micro device bonding layer and abonding layer 140.

In addition to bonding layers 140, the embodiments illustrated in FIGS.1A-1C include a repair bonding site 401 within each bank opening 128that is large enough to receive a micro LED device. In this manner, theplurality of bonding layers 140 and repair bonding site 401 create aredundancy and repair configuration within each bank opening 128. In theparticular embodiments illustrated in FIGS. 1A-1C the repair bondingsite 401 is illustrated as being a bare surface on the reflective banklayer 142. However, embodiments of the invention are not limited tosuch. In other embodiments, the repair bonding site 401 may also includea bonding layer 140 similarly as the other two bonding layers 140described and illustrated for the preexisting redundancy scheme.Accordingly, in some embodiments, bonding layers 140 are provided on thereflective bank layer 142 at the sites of all of the intended micro LEDdevices in the redundancy scheme, as well as at the repair site 401.

In the embodiments illustrated an arrangement of ground tie lines 144may run between bank openings 128 in the pixel area 104 of the displaypanel 100. In addition, a plurality of openings 149 expose the pluralityof ground tie lines 144. The number of openings 149 may or may not havea 1:1 correlation to the number of columns (top to bottom) of bankopenings 128. For example, in the embodiment illustrated in FIG. 1A, aground tie opening 149 is formed for each column of bank openings 128,however, this is not required and the number of ground tie openings 149may be more or less than the number of columns of bank openings 128.Likewise, the number of ground tie lines 144 may or may not have a 1:1correlation to the number of rows (left to right) of bank openings. Forexample, in the embodiment illustrated a ground tie line 144 is formedfor every two rows of bank openings 128, however, this is not requiredand the number of ground tie lines 144 may have a 1:1 correlation, orany 1:n correlation to the number (n) of rows of bank openings 128.

While the above embodiments have been described and illustrated withground tie lines 144 running left and right horizontally across thedisplay panel 100, embodiments are not so limited. In other embodiments,the ground tie lines can run vertically, or both horizontally andvertically to form a grid. A number of possible variations areenvisioned in accordance with embodiments of the invention. Inaccordance with embodiments of the invention, ground tie lines areformed between the bank openings 128 in the pixel area and areelectrically connected to the ground ring 116 or ground line in thenon-display area. In this manner, the ground signal may be moreuniformly applied to the matrix of subpixels, resulting in more uniformbrightness across the display panel 100. In addition, by forming theground tie lines 144 from a material having better electricalconductivity than the top electrode layer (which is yet to be formed),this may reduce the contact resistance in the electrical ground path.

It is to be appreciated, that the specific arrangement of vertical microLED devices 400 with ground tie lines 144 illustrated in FIGS. 1A-C isexemplary and that embodiments of the invention may also be practicedwith other micro LED devices. For example, FIG. 1D illustratesalternative micro LED devices 400 transferred and bonded to displaysubstrate 102 similarly as described above with regard to FIG. 1C.Similar to the micro LED devices of FIG. 1C, the micro LED devices inFIG. 1D includes a micro p-n diode including doped layers 405, 409opposite one or more quantum well layers 416. Unlike the micro LEDdevices of FIG. 1C, the micro LED devices in FIG. 1D includes bottomcontacts to both the doped layers 405, 409. For example, bottom contact404 is formed on doped layer 405, and bottom contact 403 is formed ondoped layer 409. A conformal dielectric barrier layer 407 may also beoptionally formed on the micro LED devices of FIG. 1D, particularly toprotect sidewalls 406 including the quantum well layer(s) 416. Since themicro LED devices 400 of FIG. 1D includes bottom contacts for both then-doped and p-doped layers, the reflective layer 142 may also beseparated into two electrically separate layers to make electricalcontact with bottom contacts 404, 403, respectively. Accordingly, themicro LED device of FIG. 1D may be implemented within embodiments of theinvention where it is not required to have top and bottom contacts, andthe micro LED devices can be operably connected with bottom contacts.

Referring now to FIGS. 2A-2D isometric view illustrations are providedfor arrangements of micro LED devices mounted within a reflective banklayer of a subpixel 108 in accordance with embodiments of the invention.FIG. 2A illustrates a reflective bank layer 142 formed along thesidewalls and bottom surface of the bank openings 128 as previouslydescribed above, and partially along the top surface of the patternedbank layer 126 adjacent the bank openings 128. In the embodimentillustrated in FIG. 2A, a pair of micro LED devices 400 are mountedwithin the reflective bank layer 142 such that they are evenly spacedfrom opposite sidewalls along the length of the bank opening.Accordingly, FIG. 2A is illustrative of an exemplary micro LED deviceredundancy scheme. In the embodiment illustrated in FIG. 2B, a pair ofmicro LED devices 400 are mounted within the reflective bank layer 142so that there is room for an additional micro LED device at a repairbonding site 401. Accordingly, FIG. 2B is illustrative of an exemplarymicro LED device redundancy scheme with repair site.

In practical application, it is not expected to always achieve 100%transfer success of the micro LED devices 400 from a carrier substrateto the display substrate 102, and with no defective, missing, orcontaminated micro LED devices. In accordance with embodiments of theinvention, micro LED devices may be of 1 to 100 μm in scale, forexample, having a maximum width of approximately 20 μm, 10 μm, or 5 μm.Such micro LED devices are fabricated so that they are poised for pickup from a carrier substrate and transfer to the display substrate, forexample, using an array of electrostatic transfer heads. Defective microLED devices may result from a variety of reasons, such as contamination,stress fractures, and shorting between conductive layers. Micro LEDdevices also may not be picked up during the transfer operation due to avariety of reasons, such as non-planarity of the carrier substrate,contamination (e.g. particulates), or irregular adhesion of the microLED devices to the carrier substrate. After the micro LED device 400transfer operations are completed, testing can be performed to detectdefective, missing, or contaminated micro LED devices and determine ifany repair operations need to be performed.

FIGS. 2C-2D illustrate exemplary applications of placing an additionalmicro LED device at the repair site after a defective, missing, orcontaminated micro LED device is detected. For example, following thetransfer and bonding of micro LED devices 400 shown in FIG. 2B the microLED devices transferred to the display substrate can be inspected. If itis found that a micro LED device 400X is defective or contaminated, arepair micro LED device 400 can then be bonded at the repair site 401 asillustrated in FIG. 2C. Alternatively, it is found that a micro LEDdevice was not transferred to an intended bonding site, a repair microLED device 400 can then be bonded at the repair site 401 as illustratedin FIG. 2D.

Referring now to FIGS. 3A-3C isometric view illustrations are shown ofarrangements of micro LED devices mounted within a reflective bank layerof a subpixel with separate wavelength conversion layers formed overindividual micro LED devices in accordance with embodiments of theinvention. As shown in FIG. 3A a separate wavelength conversion layer310 is formed over each of the individual micro LED devices 400 of apair of micro LED devices. As shown in FIG. 3B a repair micro LED device400 has been transferred to the reflective bank layer 142 and a separatewavelength conversion layer 310 is formed over each of the individualmicro LED devices 400 of a pair of micro LED devices. In thisconfiguration, a wavelength conversion layer 310 has not been formedover a defective or contaminated micro LED device 400X. FIG. 3C issimilar to that of FIG. 3B, except that a wavelength conversion layer isnot formed over the bonding layer 140 corresponding to a missing microLED device.

FIGS. 4A-4C show isometric view illustrations of an arrangement of microLED devices mounted within a reflective bank layer of a subpixel with asingle wavelength conversion layer formed over the micro LED devices inaccordance with embodiments of the invention. The arrangement of themicro LED devices in FIGS. 4A-4C is the same as the exemplaryarrangements shown in FIGS. 3A-3C, with the difference being that asingle wavelength conversion layer 310 is formed over all of the microLED devices 400 within the subpixel, or within reflective bank layer142. As shown in FIGS. 4B-4C, the wavelength conversion layer 310 mayalso be formed over a defective or contaminated micro LED device 400X,or a bonding layer 140 corresponding to a missing micro LED device.

In the embodiments illustrated in FIGS. 4A-4C, the wavelength conversionlayer 310 is illustrated as being within the reflective bank layer 142within the subpixel, however, in other embodiments the wavelengthconversion layer 310 is formed over the entire reflective bank layer 142as illustrated in FIG. 5. In other embodiments, the wavelengthconversion layer 310 is formed over at least the bottom surface andsidewalls of the reflective bank layer 142. A black or white matrixmaterial can be formed over portions of the reflective bank layer 142formed on top of the patterned bank layer 126. In this manner all lightemitted from the micro LED devices within the reflective bank layer 142that is visible by the viewer passes through the wavelength conversionlayer. In addition, such a configuration requires reflected light fromother sources, such as outside of the display, to pass through thewavelength conversion layer 310. It is to be appreciated, that whileFIG. 5 illustrates the micro LED device 400 pair configuration of FIG.2B, that the wavelength conversion layer 310 of FIG. 5 can be formedover any micro LED device configuration mounted within the reflectivebank layer 142, including, for example, those previously illustrated inFIG. 2A, FIG. 2C, and FIG. 2D.

Thus far the wavelength conversion layer 310 in FIG. 3A-FIG. 5 have beenillustrated as being in a dome shaped configuration, which can be formedfrom the wavelength conversion layer 310, and optionally additionallayers. For example, a light distribution layer can be formed underneaththe wavelength conversion layer as will be described in further detailin the following description. The dome shape profile may behemispherical, flattened, or narrowed. For example, a hemisphericalprofile may improve light extraction and create a Lambertian emissionpattern. Flattening or narrowing of the dome profile can be used toadjust viewing angle for the light emitting device. In accordance withembodiments of the invention, the thickness and profile the layers canbe adjusted in order to change the light emission beam profile from themicro LED devices, as well as color over angle characteristics of thedisplay which can be related to edge effects.

Referring now to FIGS. 6A-8B, a variety of configurations areillustrated including an elongated dome shaped wavelength conversionlayer, which can be formed from the wavelength conversion layer 310, andoptionally additional layers. For example, a light distribution layercan be formed underneath the wavelength conversion layer as will bedescribed in further detail in the following description. In thismanner, the light distribution layer can function as a light pipe toincrease the fill factor for the micro LED devices within the reflectivebank layers.

FIGS. 6A-6C show isometric view illustrations of an arrangement of microLED devices mounted within a reflective bank layer of a subpixel with asingle elongated wavelength conversion layer formed over the micro LEDdevices in accordance with embodiments of the invention. The arrangementof the micro LED devices in FIGS. 6A-6C is the same as the exemplaryarrangements shown in FIGS. 3A-3C, with the difference being that asingle elongated wavelength conversion layer 310 is formed over all ofthe micro LED devices 400 within the subpixel, or within reflective banklayer 142. As shown in FIGS. 6B-6C, the elongated wavelength conversionlayer 310 may also be formed over a defective or contaminated micro LEDdevice 400X, or a bonding layer 140 corresponding to a missing micro LEDdevice.

In the embodiments illustrated in FIGS. 6A-6C, the wavelength conversionlayer 310 is illustrated as being only on the bottom surface of thereflective bank layer 142 within the subpixel. FIG. 7A illustrates anembodiment in which the wavelength conversion layer 310 is formed overat least the bottom surface and sidewalls of the reflective bank layer142. FIG. 7B illustrates an embodiment in which the wavelengthconversion layer 310 is formed over the entire reflective bank layer142. In this manner all light emitted from the micro LED devices withinthe reflective bank layer 142 that is visible by the viewer passesthrough the wavelength conversion layer. The configuration illustratedin FIG. 7B requires light that is reflected by the reflective bank layer142 originating from sources other than the micro LED device, such asoutside of the display, to pass through the wavelength conversion layer310. In the configurations illustrated in FIGS. 6A-6C and FIG. 7A ablack or white matrix material can be formed over portions of thereflective bank layer 142 formed on top of the patterned bank layer 126.It is to be appreciated, that while FIGS. 7A-7B illustrate the micro LEDdevice 400 pair configuration of FIG. 2B, that the wavelength conversionlayer 310 of FIGS. 7A-7B can be formed over any micro LED deviceconfiguration mounted within the reflective bank layer 142, including,for example, those previously illustrated in FIG. 2A, FIG. 2C, and FIG.2D.

Up until this point, configurations have been illustrated in which awavelength conversion layer is formed over a single reflective banklayer 142. In the embodiments illustrated in FIGS. 8A-8B a wavelengthconversion layer is illustrated as being formed over or spanningmultiple reflective bank layers 142. For example, each reflective banklayer 142 can correspond to a subpixel within a pixel. FIG. 8A is anisometric view illustration of a pixel including an elongated domeshaped wavelength conversion layer 310 formed over multiple reflectivebank layers 142 corresponding to multiple subpixels in accordance withan embodiment of the invention. As illustrated, the wavelengthconversion layer 310 may be formed over all of the reflective banklayers 142 within a pixel. FIG. 8B is an isometric view illustration ofa pixel including both an elongated dome shaped wavelength conversionlayer 310 formed over multiple reflective bank layers 142 correspondingto multiple subpixels and an elongated dome shaped wavelength conversionlayer 310 formed over a single reflective bank layer 142 correspondingto a single subpixel in accordance with an embodiment of the invention.

Up until this point the wavelength conversion layers 310 have beenillustrated as single layer systems. In some embodiments, a number ofadditional layers can be formed under or over the wavelength conversionlayers. For example, the wavelength conversion layers may be included ina micro lens configuration that may be shaped to change the lightemission beam profile from the micro LED devices 400.

Referring now to FIG. 9A a combination view is provided of a lightdistribution layer in the form of a light pipe around a micro LED deviceand wavelength conversion layer over the light pipe in accordance withan embodiment of the invention. FIG. 9A is referred to as a combinationview because it includes characteristics of an isometric view, plan viewfor location of the micro LED device, and cross-sectional view of thelayers. In the following embodiments description is made with regard toa specific vertical micro LED device 400 structure. It is to beappreciated, that the specific micro LED device 400 illustrated isexemplary and that embodiments of the invention are not limited. Forexample, embodiments of the invention may also be practiced with LEDdevices such as those described and illustrated with regard to FIG. 1D.The following description is also made with regard to a lightdistribution layer 320 in the form of a light pipe. It is to beappreciated that such a configuration has been selected in order toadequately describe numerous possible arrangements of layers and shapes,and that the arrangements of layers can also be used to form any of theprofiles previously described, such as dome shaped and elongated domeshaped, among others.

As shown in FIGS. 9A a light distribution layer 320 is optionally formedaround one or more micro LED devices 400 prior to forming the wavelengthconversion layer 310. As described herein a layer “around” a micro LEDdevice may be formed laterally to, over, or below the micro LED device.Thus, the term “around” a micro LED device does not require the layer tobe located at all directions from the micro LED device. Rather, the term“around” is intended to refer to a neighboring area through which thelight emission beam path from the micro LED device is designed to passthrough. In the particular embodiment illustrated in FIG. 9A, the lightpipe around the micro LED devices 400 is both lateral to and over themicro LED devices.

A light distribution layer 320 in the form of a light pipe may be shapedto both allow refraction of incident light from the micro LED devices400 out of the light pipe and toward a wavelength conversion layer 310,and to cause internal reflection and lateral spreading of incident lightfrom the micro LED devices 400 within the light distribution layer 320.The light distribution layer 320 may be thicker than the micro LEDdevice 400. In an embodiment, the light distribution layer 320 is 1μm-100 μm thick. The lateral length/width of the light distributionlayer may be greater than the thickness of the light distribution layerin order to support lateral spreading of the incident light. In anexemplary embodiment, considering a 100 μm×100 μm wide subpixel, a lightdistribution layer 320 may have a lateral length of 100 μm, a lateralwidth of 100 μm and a height that is equal to or less than the maximumlateral length or width.

The light distribution layer 320 may also be dome shaped to createradial spreading of the light refracted out of the light pipe. The domeshape profile may be hemispherical. The dome shape may also be flattenedor narrowed. In some embodiments, the light distribution layer 320 iselongated dome shaped. In an embodiment, the thickness and profile ofthe light distribution layer 320 provides a base structure upon which amicro lens structure is formed in order to change the light emissionbeam profile from the micro LED devices 400, as well as color over anglecharacteristics of the display which can be related to edge effects.Light distribution layer 320 may be formed of a variety of transparentmaterials such as epoxy, silicone, and acrylic, which have the followingreported refractive indices (n) at nominal 590 nm wavelength:n=1.51-1.57 (epoxy), n=1.38-1.58 (silicone), n=1.49 (acrylic). In anembodiment, light distribution layer 320 is formed by ink jet printing.In an embodiment, the light distribution layer 320 is formed byapplication of a molten glass. Glass compositions can range from avariety of compositions ranging from acrylic glass, crown glass, flintglass, and borosilicate glasses that possess indices of refraction thatcan be matched to those of a matrix material forming the wavelengthconversion layer 310 such as epoxy, silicone, or acrylic. The particularprofile of the light distribution layer 320 can be created throughseveral processing techniques. One way is by tailoring surface tensionon in ink printed materials. Lithography or other wafer-level opticstechniques such as those used to form micro lenses may also be used.Physical techniques such as moulding or imprint lithography may also beused.

FIG. 9B is a cross-sectional side view illustration of a lightdistribution layer in the form of a light pipe around a micro LED deviceand a wavelength conversion layer over the light pipe in accordance withan embodiment of the invention. As shown in FIG. 9B, incident lightemitting from the micro LED devices 400 can both be refracted out of thelight distribution layer 320 and into the wavelength conversion layer310, and also reflected internally within the light distribution layer320 to cause lateral spreading of the incident light from the micro LEDdevices where the reflected light is eventually refracted out of thelight distribution layer 320 and into the wavelength conversion layer310. FIGS. 9C-9D are cross-sectional side view illustrations of a lightdistribution layer in the form of a light pipe and having a taperedprofile in accordance with embodiments of the invention. In theparticular embodiment illustrated in FIG. 9C, the light distributionlayer 320 is tapered toward the lateral edges so that the lightdistribution layer is thinner at the edges than the middle. Tapering thethickness of the light distribution layer 320 can result in increasereflection, causing the light to eventually refract through the topsurface of the light distribution layer rather than through the edges.In the embodiment illustrated in FIG. 9D, the pair of micro LED devicesare placed nearer one edge of the light distribution layer 320, which istapered from one side to the other. In this manner, the lightdistribution layer 320 can guide the light from one side of the lightdistribution layer to the other where the light is refracted through thetop surface rather than through a side of the light distribution layer.

In addition to allowing refraction and reflection of incident light fromthe micro LED devices 400, light distribution layer 320 may also allowthe light emitting from the micro LED devices 400 to spread out prior toentering the wavelength conversion layer 310, which decreases theoptical intensity of light entering the wavelength conversion layer. Inone aspect, the internally reflected light allows for an improved fillfactor of the micro LED devices 400, pixel, or subpixel including themicro LED devices. In another aspect, the spread out light (includingincident light not reflected, as well as reflected light) may result inmore even emission from the wavelength conversion layer 310 to be formedover the light distribution layer. In another aspect, the lightdistribution layer 320 may function to increase the length that lighttravels in the device before being emitted. This can result in areduction of the optical density and reduce thermal degradation of thephosphor particles in wavelength conversion layer, prolonging lifetimeof the display device. This may also increase the chances of colorconversion by the phosphor particles in the wavelength conversion layerwithout having to increase the volume loading of the phosphor particlesin the wavelength conversion layer. In yet another aspect, spreading outof the light and reduction of the optical intensity may reduce theamount of back reflection from the wavelength conversion layer thatcould otherwise be reabsorbed by the micro LED devices 400. Inaccordance with embodiments of the invention, light distribution layer320 may increase the fill factor, increase total light emission,increase emission uniformity, and increase sharpness of the colorspectrum for the display device. The thickness and profile of the lightdistribution layer may also provide a base structure from which a microlens structure is formed in order to change the light emission beamprofile from the micro LED devices 400, as well as color over anglecharacteristics of the display which can be related to edge effects.

Following the formation of the optional light distribution layer 320, amatching layer 322 may optionally be formed over the light distributionlayer 320 prior to forming the wavelength conversion layer 310. Thematching layer 322 may function to match the indices of refraction forthe light distribution layer 320 and wavelength conversion layer 310 toreduce back reflection of light. For example, where layers 320, 310 areformed of, for example, an epoxy, silicone, acrylic, or glass havingdifferent indices of refraction, the matching layer 322 is formed of anepoxy, silicone, acrylic, or glass having an index of refraction betweenthat of layers 320, 310. In accordance with embodiments of theinvention, the polymer matrix forming layers 320, 310 is the same, andlayers 320, 310 have an identical index of refraction. In anotherembodiment, the index of refraction for layers 320, 310 is within 0.3,or more particularly within 0.1. In an embodiment, matching layer is 2μm or less in thickness. In an embodiment, curing of the matching layer322 may be thermal or UV.

In accordance with embodiments of the invention, a wavelength conversionlayer 310 is formed over the micro LED devices 400 and over the optionallight distribution layer 320 and matching layer, if present. In anembodiment, the wavelength conversion layer includes phosphor particlesto control the light emission spectrum. In one embodiment, thewavelength conversion layer includes different phosphor particles(different in designed size or shape, or composition) for a blendedcolor emission spectrum (e.g. a combination of any of red, blue, green,yellow, etc). In another embodiment, the wavelength conversion layerincludes phosphor particles designed for a single color emissionspectrum (e.g. red, blue, green, yellow, etc).

In an embodiment, the wavelength conversion layer 310 is formed ofphosphor particles. For example, the wavelength conversion layer isformed of a spray deposition method followed by removal of solvents. Inan embodiment, the wavelength conversion layer includes a dispersion ofphosphor particles in a matrix material such as a polymer or glassmatrix material. Other filler materials such as pigment, dye, orscattering particles may also be dispersed within the matrix or amongthe phosphor particles themselves if no matrix material is present. Inan embodiment, wavelength conversion layer 310 is formed by ink jetprinting, and UV cured. In an embodiment, the wavelength conversionlayer 310 is formed by application of a molten glass, where the fillersare thermally and chemically stable within the molten glass. Thethickness of the wavelength conversion layer 310, as well aconcentration of fillers, e.g. phosphor particles, pigment, dye, orlight scattering particles are tuned to achieve the requisite colorspectrum. For example, in an embodiment the thickness and concentrationis tuned to minimize color bleeding from the micro LED devices throughthe wavelength conversion layer, and maximize emission from the phosphorparticles. Thickness of the wavelength conversion layer 310 (as well aslight distribution layer) may also be partly determined by the spacingbetween micro LED devices. For example, micro LED devices may be spacedmore closely together in high resolution display applications comparedto lighting applications. In an embodiment, the wavelength conversionlayer 310 is 5 μm-100 μm thick, or more specifically 30 μm-50 μm thickfor an exemplary 5 μm wide and 3.5 μm tall micro LED device 400. In someembodiments, the thickness of the wavelength conversion layer andconcentration of fillers may be designed to allow some light from themicro LED devices 400 to pass through resulting a mix of the micro LEDdevice light spectrum and the converted light spectrum to achieve ablended emission spectrum, for example, white light. Concentration ofthe color converting materials (e.g. phosphor particles, pigment, dye)as well as thickness of the layers can depend upon the particularapplication of the light emitting device, for example, if full colorconversion (e.g. from blue to red, or blue to green, etc.) is to occur,if leakage or bleeding of light from the underlying micro LED devices isto occur, or if a mixture of converting materials is employed. In anembodiment where full color conversion (e.g. from blue to red, or blueto green, etc.) occurs a volume loading percent of greater than 50%color converting materials may be included in the wavelength conversionlayer. In an embodiment, the wavelength conversion layer includesgreater than 50% volume loading of phosphor particles. The lightdistribution layer 320 can function to increase the length that lighttravels in the device before being emitted in order to increase thechances of color conversion by the phosphor particles in the wavelengthconversion layer 310 without having to increase the volume loading ofthe phosphor particles in the wavelength conversion layer.

In accordance with embodiments of the invention, the term “phosphor” mayrefer to any type of wavelength converting material that will absorblight at one wavelength and emit light at another wavelength. One typeof phosphor particle is a quantum dot. Quantum dots are semiconductormaterials where the size of the structure is small enough (less thantens of nanometers) that the electrical and optical characteristicsdiffer from the bulk properties due to quantum confinement effects. Forexample, the emission properties of quantum dots are related to theirsize and shape in addition to their composition. Fluorescence of quantumdots is a result of exciting a valence electron by absorbing a certainwavelength, followed by the emission of lower energy in the form ofphotons as the excited electrons return to the ground state. Quantumconfinement causes the energy difference between the valence andconduction bands to change based on size and shape of the quantum dotmeaning that the energy and wavelength of the emitted photons isdetermined by the size and shape of the quantum dot. The larger thequantum dot, the lower the energy of its fluorescence spectrum.Accordingly, smaller quantum dots emit bluer light (higher energy) andlarger quantum dots emit redder light (lower energy). This allowssize-dependent tuning of the semiconductor photoluminescence emissionwavelength throughout the visible spectrum, with a sharp emissionspectrum and high quantum efficiency.

Examples of quantum dot materials include, but are not limited to,groups II-VI, III-V, IV-VI semiconductor materials. Some exemplarycompound semiconductors include CdS, CdSe, CdTe, ZnS, ZnSe, ZnTe, GaAs,GaP, GaAs, GaSb, HgS, HgSe, HgTe, InAs, InP, InSb, AlAs, AlP, AlSb. Someexemplary alloyed semiconductors include InGaP, ZnSeTe, ZnCdS, ZnCdSe,and CdSeS. Multi-core structures are also possible. Exemplary multi coreconfigurations may include a semiconductor core material, a thin metallayer to protect the core from oxidation and to aid lattice matching,and a shell to enhance the luminescence properties. The shell mayfunction to absorb light at a specific spectrum that is different fromthe emission spectrum from the quantum dot. The core and shell layersmay be formed of the same material, and may be formed of any of theexemplary compound semiconductors or alloyed semiconductors listedabove. The metal layer often comprises Zn or Cd.

In accordance with embodiments of the invention, one type of phosphorparticle is a particle that exhibits luminescence due to itscomposition. Some exemplary phosphor particles that exhibit luminescencedue to their composition include sulfides, aluminates, oxides,silicates, nitrides, YAG (optionally doped with cerium), and terbiumaluminum garnet (TAG) based materials. Other exemplary materials includeyellow-green emitting phosphors: (Ca,Sr,Ba)Al₂O₄:Eu (green), (Lu,Y)₃Al₅O₁₂:Ce³⁺ (LuAG, YAG) (yellow-green), Tb₃Al₅O₁₂:Ce³⁺ (TAG)(yellow-green); orange-red emitting phosphors: BaMgAl₁₀O₁₇:Eu²⁺ (Mn²⁺),Ca₂Si₅N₈:Eu²⁺ (orange-red), (Zn,Mg)S:Mn (green, red), (Ca,Sr,Ba)S:Eu²⁺(red); uv-deep blue absorbing phosphors for blue and yellow-greenemission: (Mg,Ca,Sr,Ba)₂SiO₄:Eu²⁺ (uv-blue excitation, yellow emission),(Mg,Ca,Sr,Ba)₃Si₂O₇:Eu²⁺ (uv-deep blue excitation, blue-green emission),Ca₈Mg(SiO₄)₄Cl₂:Eu²⁺ (uv-deep blue excitation, blue emission); andphosphors that can emit over the full visible spectrum depending oncomposition and processing (Sr,Ca,Ba)Si_(x)O_(y)N_(z):Eu²⁺ (y>0 green,y=0 red), Y₂O₂S:Eu³⁺ (blue-green),(Ca,Mg,Y)_(v)Si_(w)Al_(x)O_(y)N_(z):Eu² (yellow-green-red). In someembodiments the particle size for such phosphor particles may be from 1μm to 20 μm. In other embodiments, the particles size for such phosphorparticles can be nanoparticles from 100 nm to 1 μm. The phosphorparticles can also include a blend of the 1 μm to 20 μm particles and100 nm to 1 μm nanoparticles. Nanoparticles may be useful, for example,to reduce the amount of settling when dispersed within a matrix materialof a wavelength conversion layer prior to curing or solvent removal,which may result in more even distribution of the nanoparticles andlight emission of the light emitting device.

Other materials may also be dispersed within the wavelength conversionlayer. For example, the other materials may be dispersed within thematrix material, such as glass or polymer matrix of the wavelengthconversion layer. In an embodiment, a light scattering agent such asTiO₂ or Al₂O₃ particles is dispersed within the wavelength conversionlayer. Such light scattering agents may have the effect of increasingthe phosphor particle efficiency by increasing scattered light withinthe wavelength conversion layer. Such light scattering agents mayadditionally have the effect of reduced bleeding of the micro LED deviceemitted light through the wavelength conversion layer. Light scatteringparticles can also be used to control when and where light is emittedfrom the micro lens structure. For example, a higher concentration oflight scattering particles can be placed at the ends of the micro lensstructure, e.g. at lateral edges of the wavelength conversion layer, todirect the light out. In an embodiment, a pigment or dye may bedispersed within the wavelength conversion layer 310. This may have theeffect of incorporating a color filter into the wavelength conversionlayer. In an embodiment, the pigment or dye may have a color similar tothe emission wavelength of the phosphor particle. In this manner, thepigment or die can absorb wavelengths other than those being emittedfrom the phosphor particle, further sharpening the emission spectrum ofthe assembly. For example, in a particular embodiment, the micro LEDdevice 400 is a gallium nitride (GaN) based material, and emits a blue(e.g. 450 nm-495 nm) or deep blue (e.g. 420 nm-450 nm) light. Quantumdots designed for red emission may be dispersed in the wavelengthconversion layer 310 in order to absorb the blue or deep blue emissionfrom the micro LED device 400 and convert the emission wavelength tored. In such an embodiment, a red pigment or dye may also be dispersedwithin the wavelength conversion layer 310 to also absorb colors otherthan red. In this manner, the red pigment or dye may absorb additionalblue or deep blue light, thereby reducing bleeding of the unconvertedblue or deep blue light. Exemplary pigments include lithol rubine (Red),B-copper thalocyanine (Blue), and diarylide yellow (Yellow). It is to beappreciated that a blue micro LED device and red phosphor particles withred pigment or dye is exemplary and a variety of emission spectrumconfigurations for the micro LED devices and wavelength conversionlayers, where present, are possible.

In accordance with some embodiments of the invention, the polymer matrixforming the wavelength conversion layer 310 may be permeable to oxygenor moisture. In an embodiment, following the formation of the wavelengthconversion layer 310, an oxygen barrier film 324 may optionally beformed in order to protect the wavelength conversion layer 310 fromoxygen or moisture absorption. For example, where wavelength conversionlayer 310 includes quantum dots, the oxygen barrier film 324 can act asa barrier to oxygen or moisture absorption by the quantum dots, therebyprolonging the lifetime of the quantum dots in the display device.Suitable materials for the oxygen barrier film 324 include, but are notlimited to, Al₂O₃, SiO₂, SiN_(x), and glass. The deposition method foroxygen barrier film 324 may be a low temperature method in order to notthermally degrade the quantum dots or other fillers. Exemplary conformaldeposition methods include atomic layer deposition (ALD), sputtering,spin on, and lamination. The oxygen barrier film may also be blanketdeposited over the entire substrate, or over all of the micro LEDdevices. In an embodiment, an Al₂O₃ oxygen barrier film is deposited byatomic layer deposition (ALD).

Referring now to FIGS. 10A-10C, combination and cross-sectional sideview illustrations are provided for embodiments including reflectivelayers 330 directly over the micro LED devices 400 where lightdistribution layer 320 is in the form of a light pipe. Reflective layers330 can be provided in different locations, which may result indifferent effects on the light pipe and wavelength conversion layerconfiguration. In one embodiment illustrated in FIG. 10B the reflectivelayers 330 are formed over the wavelength conversion layer 310. In thismanner, the reflective layer can block incident light emitted from themicro LED devices 400 from bleeding through the wavelength conversionlayer 310 at the closest location to the micro LED devices, whereoptical intensity may be the greatest. Reflection of the incident lightcan also have the effect of laterally spreading the light therebyimproving the fill factor. Another effect of the reflective layers 330may also be to increase the number of passes of the incident lightthrough the wavelength conversion layer. By way of example, situationsare illustrated where the incident light passes through the wavelengthconversion layer 310 three times and five times. With each pass,phosphor particles are excited and emit converted spectra. In thismanner, the efficiency of the phosphor particles in the wavelengthconversion layer 310 can be improved, thereby increasing the convertedspectra light intensity of the system, while also improving the fillfactor, and providing more even emission from the wavelength conversionlayer 310.

In another embodiment illustrated in FIG. 10C reflective layers 330 areformed between the light distribution layer 320 and the wavelengthconversion layer 310. In such a configuration, the reflective layer mayinfluence lateral spreading of incident light, and improve the fillfactor. Such a configuration may also block incident light from enteringthe wavelength conversion layer 310 at the closest location to the microLED devices, where optical intensity may be the greatest. As such,bleeding of incident light through the wavelength conversion layer 310can be reduced. This configuration may also increase the lifetime of thephosphor particles, particularly where optical intensity would have beenthe greatest.

FIGS. 10D-10F illustrate embodiments similar to those illustrated anddescribed with regard to FIGS. 10A-10C. In the embodiments illustratedin FIGS. 10D-10F, a reflective layer 330 is formed over a micro LEDdevice 400 pair including a repair micro LED device, and optionally notformed over a missing, defective, or contaminated micro LED device 400X.Alternatively, a reflective layer can also be formed over a missing,defective, or contaminated micro LED device 400X.

The reflective layers 330 described above and illustrated in FIGS.10A-10F are illustrated as being flat layers. However, it is notrequired that the reflective layers 330 are flat. Any configuration ispossible, and the reflective layers 330 may be shaped to control thedirection of light emission. Reflective layers 330 also are not requiredto be formed directly above the micro LED devices, and may be formed atother locations such as along the lateral edges of the light pipe orwavelength conversion layer.

In accordance with embodiments of the invention, the light emittingdevice configurations including the micro LED devices and wavelengthconversion layers can be incorporated into a variety of display devices.Exemplary display applications include display signage, display panels,televisions, tablets, phones, laptops, computer monitors, kiosks,digital cameras, handheld game consoles, media displays, ebook displays,or large area signage display.

The wavelength conversion layers can be designed to all emit the samecolor emission spectrum, or the wavelength conversion layers can bedivided into multiple groups of wavelength conversion layers, with eachgroup designed to emit a different color emission spectrum. In thismanner, the displays can emit any color or patterns of colors dependingupon the arrangement and content of the micro LED devices and wavelengthconversion layers. In one embodiment, white light can be generated byincorporating red (e.g. 620 nm-750 nm) and green (e.g. 495 nm-570 nm)emitting phosphor particles in a wavelength conversion layer positionedover a blue emitting (e.g. 450 nm-495 nm) micro LED device. In anotherembodiment, white light can be generated by incorporating multiple microLED devices into a pixel, with each micro LED device designed to emitthe same emission spectrum (e.g. visible spectrum or UV spectrum), anddifferent wavelength conversion layers designed to convert coloremission. In this manner, by including phosphor particles of a singlecolor emission spectrum over each light distribution layer, secondaryabsorption of light emitted from different emission spectra of differentphosphor particles is avoided. This may increase efficiency and reduceunintended color shift.

Referring now to FIG. 11A, a combination view illustration is providedof a display including a plurality of micro LED devices 400 bonded to adisplay substrate 102, a plurality of light distribution layers 320 inthe form of light pipes around the plurality of micro LED devices 400,and a plurality of wavelength conversion layers 310 over the pluralityof light distribution layers 320. In the particular embodimentillustrated, a pixel 106 includes a plurality of micro LED devices 400within light distribution layers 320 and wavelength conversion layers310 designed to convert emission, e.g. in an RGB subpixel arrangement.In an embodiment, a black matrix material 202 can be formed over thesubstrate 102 and between the light pipes to absorb light and preventcolor bleeding into adjacent pixels 106 or subpixels 108. Alternatively,the black matrix material 202 can be substituted with a white matrixmaterial to reflect light and prevent color bleeding into adjacentpixels 106 or subpixels 108.

When arranged in a pixel configuration, each subpixel 108 may contain asingle phosphor color emission, where present. Each subpixel maylikewise contain a different phosphor color emission, where present. Inthis manner, secondary absorption of light emitted from a phosphorparticle emitting a different spectrum (e.g. absorption of green lightemitted from a green emitting phosphor particle by a red emittingphosphor particle) is avoided. This may increase efficiency and reduceunintended color shift. Such pixel and subpixel configurations can beused for the final output of white light, or any other color of light.

For example, a pixel may contain 3 micro LED devices in 3 light pipes,or a pair of micro LED devices in each light pipe, with all the microLED devices designed to emit blue light, with one red emittingwavelength conversion layer over one light pipe, one green emittingwavelength conversion layer over a second light pipe, and the thirdlight pipe either not including a wavelength conversion layer over it orincluding a blue emitting wavelength conversion layer over it. In oneembodiment, white light can be generated by incorporating multiple microLED devices into a pixel, with each micro LED device designed to emit UVlight, with one red emitting conversion layer over a first light pipe,one green emitting wavelength conversion layer over a second light pipe,and one blue emitting wavelength conversion layer over a third lightpipe. In another embodiment, white light can be generated byincorporating combinations of micro LED devices designed for differentemission spectrum and different wavelength conversion layers, or nowavelength conversion layers. In another exemplary embodiment, whitelight can be generated with a light pipe around a micro LED devicedesigned for red emission with no overlying wavelength conversion layer,a light pipe around a micro LED device designed for blue emission withan overlying wavelength conversion layer designed for green emission,and a light pipe around a micro LED device designed for blue emissionwith no overlying wavelength conversion layer.

In the above exemplary embodiments, a red-green-blue (RGB) subpixelarrangement is obtained, and each pixel includes three subpixels thatemit red, green and blue lights, respectively. It is to be appreciatedthat the RGB arrangement is exemplary and that embodiments are not solimited. Examples of other subpixel arrangements that can be utilizedinclude, but are not limited to, red-green-blue-yellow (RGBY),red-green-blue-yellow-cyan (RGBYC), or red-green-blue-white (RGBW), orother subpixel matrix schemes where the pixels may have different numberof subpixels, such as the displays manufactured under the trademark namePenTile®.

FIGS. 11B-11E are schematic side view illustration of various pixelconfigurations in accordance with embodiments of the invention. Whilenot specifically illustrated, each micro LED device 400 may be one of apair of micro LED devices 400 mounted within a reflective bank layer 142of a subpixel 108, for example, as illustrated and described above withregard to FIGS. 1A-1D.

FIG. 11B is a schematic side view illustration of a pixel 106 inaccordance with an embodiment of the invention. As illustrated in FIG.11B, each micro LED device 400 is designed to emit a deep blue (DB)color spectrum. In such an embodiment, the different wavelengthconversion layers 310 can be designed to emit red (R), green (G), andblue (B) in an RGB subpixel arrangement.

FIG. 11C is a schematic side view illustration of a pixel 106 inaccordance with an embodiment of the invention. As illustrated in FIG.11C, each micro LED device 400 is designed to emit a blue (B) colorspectrum. In such an embodiment, the different wavelength conversionlayers 310 can be designed to emit red (R) and green (G). A wavelengthconversion layer 310 is not formed over the third light distributionlayer 320. In this manner an RGB subpixel arrangement is achievedwithout having to covert the blue light from the blue emitting subpixel.In an embodiment, the third light distribution layer 320 can be madethicker than the other two light distribution layers 320 over whichwavelength conversion layers 310 are formed in order to achieve similarmicro lens characteristics. For example, the thickness of the thirdlight distribution layer 320 may be similar to the total thickness ofthe first light distribution layer 320 and first red wavelengthconversion layer 310 (and any intermediate layers).

FIG. 11D is a schematic side view illustration of a pixel 106 inaccordance with an embodiment of the invention. As illustrated in FIG.11D, each micro LED device 400 is designed to emit an ultraviolet (UV)color spectrum. In such an embodiment, the different wavelengthconversion layers 310 can be designed to emit red (R), green (G), andblue (B).

FIG. 11E is a schematic side view illustration of a pixel 106 inaccordance with an embodiment of the invention. As illustrated in FIG.11E, the pixel 106 includes micro LED devices 400 designed to emit a red(R) or blue (B) color emission spectrum. As illustrated, a green (G)emitting wavelength conversion layer 310 is formed over one of the lightdistribution layers 320 around one of the blue emitting micro LED device400, and a wavelength conversion layer 310 is not required to be formedover the light distribution layers 320 formed around the red emittingmicro LED device 400 or the other blue emitting micro LED device 400.Such a configuration may be implemented, for example, when it ispossible to fabricate and integrate blue emitting and red emitting microLED devices that are more efficient than green emitting micro LEDdevices. In such an embodiment, it may be more efficient to convert bluelight to green light with a wavelength conversion layer. Such aconfiguration may also be useful when providing a broad spectrum at thevisual response peak, around 555 nm. Such a configuration may also beuseful for increasing the color rendering index (CRI), for example byusing a narrow red (or blue) emission spectrum from the micro LED devicerather than a broader phosphor particle emission spectrum. Such aconfiguration may also allow for controlling the correlated controltemperature (CCT) of the light emitting device, and hence controllingthe warmth, without losing lumens due to conversion in the red spectrum.As described above with regard to FIG. 11C, the light distribution layer320 formed around the red emitting micro LED device or the other blueemitting micro LED device in FIG. 11E may be made thicker than the otherlight distribution layer over which a wavelength conversion layer isformed in order to achieve similar micro lens characteristics.

Referring now to FIGS. 11F-11J various pixel configurations areillustrated similar to those illustrated and described above with regardto FIGS. 11A-11E with one difference being that each light distributionlayer 320 in the form of a light pipe spans across multiple subpixelswithin a pixel 106. For example, the embodiment illustrated in FIG. 11Fmay be an exemplary RGB subpixel arrangement in which a light pipe 320is formed around a micro LED device pair in each subpixel of the pixel106, however, other subpixel arrangements are possible such as, but notlimited to RGBY, RGBYC, RGBW, or others. In the particular cross-sectionillustrated, only a single micro LED device 400 of a pair isillustrated. In such arrangements the light pipe spanning acrossmultiple subpixels within a pixel allows for color mixing betweensubpixels. Such a configuration may be used in applications where themicro LED devices or subpixels are far enough apart that they couldotherwise be perceived by the human eye (e.g. approximately 100 μm ormore) and perceived as small dots. The color mixing associated with thelight pipe configurations of FIGS. 11F-11J may be used to blend themicro LED device emissions so that they are not perceived by the humaneye. One possible application may be in a heads up display where theviewing distance is short, and it is more likely that the viewer is tobe capable of perceiving emission spectra from individual subpixels ormicro LED devices.

While not specifically illustrated, each micro LED device 400 in FIGS.11G-11J may be one of a pair of micro LED devices 400 mounted within areflective bank layer 142 of a subpixel 108, for example, as illustratedand described above with regard to FIGS. 1A-1D. The arrangements ofemission spectra for the micro LED devices 400 and wavelength conversionlayers 310 is similar to that of FIGS. 11B-11E, with one differencebeing that the wavelength conversion layers 310 are formed over onlyspecific portions of the light pipe 320 shared by the micro LED devices400 in the pixel 106. Additional modifications can also be incorporatedinto the configurations illustrated in FIGS. 11G-11J. The profile of thelight pipe 320 can be altered over certain micro LED devices 400. Forexample, the light pipe 320 can be made thicker over “naked” micro LEDdevices 400 over which a wavelength conversion layer 310 is not formed.The light pipes 320 of FIGS. 11A-11J can also be tapered, for example,as previously described with regard to FIGS. 9C-9D, or includereflective layers as previously described with regard to FIGS. 10A-10F.

Referring now to FIGS. 12A-12F, various configurations for implementingmicro LED device pairs are described. The embodiments illustrated anddescribed with regard to FIGS. 12A-12F may be combinable with otherconfigurations described herein. For example, the configurationsillustrated and described with regard to FIGS. 12A-12E may be combinablewith the pixel arrangements described above with regard to FIGS.11A-11E, and the configurations illustrated and described with regard toFIG. 12F may be combinable with the pixel arrangements described abovewith regard to FIGS. 11-F-11J.

FIG. 12A illustrates a cross-sectional side view across the shorterwidth of a rectangular shaped reflective bank layer 142 illustrated inFIG. 7B, while FIG. 12B is an illustration of a longer width, orthogonalto the shorter width, of the rectangular shaped reflective bank layer142 illustrated in FIG. 7B. It is to be appreciated that the particularembodiments illustrated in FIGS. 12A-12F are provided to illustrateparticular examples for integrating micro LED device pairs in aredundancy and repair scheme, combined with a wavelength conversionlayer for a tunable color emission spectrum. The particular embodimentsillustrated include a wavelength conversion layer 310 formed over anelongated dome shaped light distribution layer 320 in the form a lightpipe, where the wavelength conversion layer 310 is also formed over thereflective bank layer 142. Furthermore, FIGS. 12A-12F illustrate varioustop electrode configurations. However, as previously described in thepreceding embodiments and figures, embodiments of the invention are notso limited. Accordingly, embodiments of the invention are not limited tothe specific combinations of the top electrode configurations andredundancy and repair schemes illustrated in FIGS. 12A-12F.

In an embodiment a pair of micro LED devices 400 are bonded to areflective bank layer 142 on or within a substrate 102 including anunderlying circuitry 210. The micro LED devices 400 can be transferredand bonded to the substrate 102 as part of an array of micro LED devices400 using a variety of techniques including a transfer bonding process,transfer using elastomeric stamps, or transfer and bonding using anelectrostatic transfer head array, as previously described. Followingthe transfer process, and prior to formation of the passivation layers316 and top electrode layers 318 illustrated in FIGS. 12A-12F thedisplay substrate 102 can be examined for defective, missing, orcontaminated micro LED devices. In this manner, detection of defective,missing, or contaminated micro LED devices can be used to potentiallyalter the deposition patterns of the passivation layer 316 and topelectrode layers 318, as well as the wavelength conversion layers, andto potentially transfer replacement micro LED devices where required.

Still referring to FIGS. 12A-12B, a sidewall passivation layer 316 canbe formed around the sidewalls of the micro LED devices 400. In anembodiment where the micro LED devices 400 are vertical LED devices, thesidewall passivation layer 316 covers and spans the quantum wellstructures 408. In accordance with embodiments of the invention, thesidewall passivation layer 316 may be transparent or semi-transparent tothe visible wavelength spectrum so as to not significantly degrade lightextraction efficiency from sidewalls of the micro LED devices 400.Sidewall passivation layer 316 may be formed of a variety of materialssuch as, but not limited to epoxy, silicone, acrylic, poly(methylmethacrylate) (PMMA), benzocyclobutene (BCB), polyimide, and polyester.In an embodiment, sidewall passivation layer 316 is formed by ink jetprinting around the light emitting devices 400, followed by curing. Inan embodiment, sidewall passivation layer 316 is cured with ultraviolet(UV) light to minimize volume change as a result of cure and protect theintegrity of the bond between the micro LED devices and the reflectivebank layer 142, though thermal curing may also be performed. Sidewallpassivation layer 316 can also be deposited using other techniques suchas slit coating, physical vapor deposition or chemical vapor depositionof a dielectric material such as a nitride or oxide, spin on techniquesuch as a spin on glass, or spray coating followed by solventevaporation. In an embodiment, sidewall passivation layer is an a-stagedor b-staged coating already formed over the substrate 102 prior tobonding the micro LED devices 400 wherein the micro LED devices punchthrough the coating during the transfer and bonding operations, and thecoating is then cured after bonding of the micro LED devices 400.

In an embodiment the sidewall passivation layer 316 at least partiallycovers the reflective bank layer 142. The sidewall passivation layer maycompletely cover the reflective bank layer 142, however, this is notrequired. Any combination of other insulating layers can be used toelectrically insulate the reflective bank layer 142 from otherelectrically conductive layers. For example, insulator layer 146 can bedeposited over edges of the reflective bank layer 142. The reflectivebank layer 142 can be discontinuous, for example, so that sidewalls arenot electrically connected to the bottom surface of the reflective banklayer 142 in electrical communication with the micro LED devices 400. Inaccordance with embodiments of the invention, a sidewall passivationlayer 316 may not be required where a conformal dielectric barrier layer107 is present along sidewalls of the micro LED devices 400.Alternatively, a sidewall passivation layer 316 may be formed incombination with an existing conformal dielectric barrier layer 107.

In embodiments including vertical micro LED device pairs, following theformation of optional sidewall passivation layer 316, a top electrodelayer 318 is formed on the micro LED device 400 pairs and in electricalcontact with the top contacts 402 and ground tie line 144. Dependingupon the particular application, top electrode layer 318 may be opaque,reflective, transparent, or semi-transparent to the visible wavelength.Exemplary transparent conductive materials include amorphous silicon,transparent conductive oxides (TCO) such as indium-tin-oxide (ITO) andindium-zinc-oxide (IZO), carbon nanotube film, or a transparentconductive polymer such as poly(3,4-ethylenedioxythiophene) (PEDOT),polyaniline, polyacetylene, polypyrrole, and polythiophene. In anembodiment top electrode layer 318 is approximately 50 nm-1 μm thickITO-silver-ITO stack, with the silver layer thin enough to betransparent to the visible wavelength spectrum. In a particularembodiment, the top electrode layer 318 is formed by ink jet printing.In an embodiment top electrode layer 318 is approximately 50 nm-1 μmthick PEDOT. Other methods of formation may include chemical vapordeposition (CVD), physical vapor deposition (PVD), or spin coatingdepending upon the desired area to be coated and any thermalconstraints.

In accordance with embodiments of the present invention, one or more topelectrode layers 318 may be used to electrically connect the micro LEDdevice 400 pairs from the array of subpixels to ground tie line 144. Avariety of configurations are possible with different redundancy andrepair configurations. In interest of clarity, FIGS. 12A-12E are limitedto exemplary top electrode layer 318 configurations within a singlesubpixel, and FIG. 12F shows an exemplary top electrode layer 318configuration within a single pixel. A more detailed description isprovided with regard to FIGS. 15-19 for various top electrode layerconfigurations across the pixel area.

Referring again to FIG. 12B, in one embodiment a single top electrodelayer is illustrated as connecting both micro LED devices 400 of thepair to ground 144/116. For example, such a configuration may be usedwhen both micro LED devices 400 have been determined to be transferredto the display substrate and not be defective or contaminated. Referringto FIG. 12C, an embodiment is illustrated where a micro LED device 400Xis determined to be defective or contaminated. In the embodimentillustrated, a repair micro LED device 400 is then bonded to thereflective bank layer 142, and one or more top electrode layers 318 arethen formed over only the operable micro LED device 400 pair toelectrically connect them to ground 144/116. FIGS. 12D-12E illustrateembodiments in which a passivation layer 316 can be formed overdefective or contaminated micro LED devices 400X, or over a bondinglayer 140 of a missing micro LED device. In the embodiment illustratedin FIG. 12D a single top electrode layer 318 is formed over the operableand defective, contaminated, or missing micro LED devices, where thepassivation layer 316 prevents electrical contact with the defective,contaminated, or missing micro LED devices. In the embodimentillustrated in FIG. 12E, one or more top electrode layers 318 are formedonly over the operable micro LED devices.

Optional wavelength distribution layer 320, optional matching layer 322,wavelength conversion layer 310, and optional barrier layer 324 may thenbe formed as described above with regard to FIG. 9A. Referring brieflyback to FIGS. 11A, 11F a black matrix (or alternatively white matrix)material 202 is illustrated between the reflective bank layers 142 inorder to block light transmission, and to separate bleeding of lightbetween adjacent subpixels. Black (or white) matrix 202 can be formedfrom a method that is appropriate based upon the material used, andcomposition of layers already formed. Manner of formation may also bedetermined by whether the black (or white) matrix is formed in a singleside manner (see FIG. 14A) or a top press down manner (see FIG. 14B).For example, black (or white) matrix 202 can be applied using ink jetprinting, sputter and etching, spin coating with lift-off, or a printingmethod. In some embodiments, black (or white) matrix 202 is formed byink jet printing and UV cured in order to not thermally degrade thephosphor particles in a wavelength conversion layer 110 already formed.Exemplary black matrix materials include carbon, metal films (e.g.nickel, aluminum, molybdenum, and alloys thereof), metal oxide films(e.g. chromium oxide), and metal nitride films (e.g. chromium nitride),organic resins, glass pastes, and resins or pastes including a blackpigment or silver particles. Exemplary white matrix materials includemetal particles or TiO₂ particles loaded within a polymer, organicresin, or glass paste, for example.

Referring again to FIGS. 12A-12E a color filter layer 328 may optionallybe formed over the wavelength conversion layer 310 to filter out colorsemitting through the wavelength conversion layer 310 other than thosedesired and to sharpen the emission spectrum of the light emittingdevice. By way of example, a red color filter layer 328 may be placedover a wavelength conversion layer 310 including red emitting phosphorparticles in order to filter out colors other than red, a green colorfilter layer 328 may be placed over a wavelength conversion layer 310including green emitting phosphor particles in order to filter outcolors other than green, and a blue color filter layer 328 may be placedover a wavelength conversion layer 310 including blue emitting phosphorparticles in order to filter out colors other than blue. Referring backto FIG. 11B, in an embodiment, a blue color filer may not be necessaryover a blue wavelength conversion layer 310 wherein the underlying microLED device 400 is deep blue emitting. Referring back to FIG. 11C, in anembodiment, a blue color filer may not be necessary over naked (e.g. nowavelength conversion layer) blue emitting underlying micro LED device400. It is to be appreciated that these configurations are exemplary anda variety of configurations are possible depending upon desired lightemission spectrum. Suitable materials for the color filter includepigments or dyes as previously described above. In an embodiment, colorfilter layer 328 includes a pigment or dye dispersed in a transparentmatrix material. In an embodiment, the matrix material is the samepolymer used for the wavelength conversion layer 310, such as epoxy,silicone, or acrylic. Likewise, the color filter may be formed usingsimilar techniques, such as ink jet printing with UV cure. In anembodiment, the wavelength conversion layer 310 has an index ofrefraction within 0.3, or more particularly within 0.1, of the index ofrefraction for the wavelength conversion layer 310. In the embodimentsillustrated in FIGS. 12A-12E the color filter layer 328 is formed afterthe black matrix 202. In other embodiments, the color filter layer 328is formed before the black matrix 202.

Referring now to FIG. 12F a cross-sectional side view illustration isprovided of a light pipe around a plurality of micro LED devices withtop and bottom contacts within a plurality of reflective bankstructures, and a wavelength conversion layer over the light pipe inaccordance with embodiments of the invention. The configurationillustrated in FIG. 12F is similar to that of FIG. 12A, with thedifference being that the light pipe 320 is formed over multiplesubpixels in a pixel, with each reflective bank layer 142 correspondingto a separate subpixel that is independently addressable by its ownunderlying circuitry 210. Similar to the other configurations, thewavelength conversion layer 310 may be wider than the openings in thepatterned bank layer 304 including the multiple reflective bank layers142.

FIGS. 13A-13B are cross-sectional side view illustrations of a lightpipe around a plurality of micro LED devices with bottom contacts withina reflective bank structure, and a wavelength conversion layer over thelight pipe in accordance with embodiments of the invention. FIG. 13C isa cross-sectional side view illustrations of a light pipe around aplurality of micro LED devices with bottom contacts within a pluralityof reflective bank structures, and a wavelength conversion layer overthe light pipe in accordance with embodiments of the invention. FIGS.13A-13C are similar to those of FIGS. 12A-12B and 12F with onedifference being that the micro LED devices 400 include bottom contacts404, 403 rather than both a bottom and top contact. As a result, it maynot be required to form a top electrode layer to contact the ground tieline 144. Sidewall passivation layer 316 also may be omitted, and thelight pipe 320 or other layers can electrically insulate the reflectivebank structure layers 142A, 142B and quantum well structure 408. Asillustrated, reflective bank structure layers 142A, 142B areelectrically insulated from one another.

Referring now to FIGS. 14A-14B, alternative cover designs are describedand illustrated for packaging the displays in accordance withembodiments. FIG. 14A is an illustration of a single side fabricationmanner for applying wavelength conversion layers and a black (or white)matrix between subpixels in accordance with an embodiment. Asillustrated, the wavelength conversion layers 310 and matrix 202 areformed on substrate 102 prior to applying a cover 500 over the lightemitting devices. Top cover 500 can be rigid or flexible, and can beapplied in a variety of manners. In an embodiment, top cover 500 is atransparent plastic material and is laminated onto the display substrate102. In an embodiment, top cover 500 is a rigid glass plate that isapplied over the light display substrate 102, and sealed around theperipheral edges of the display substrate 102 with a sealant. A gettermaterial may optionally be placed inside the sealed region containingthe micro LED devices and the wavelength conversion layer 310 to absorbmoisture, particularly if the wavelength conversion layer includesquantum dots.

FIG. 14B is an illustration of a top press down manner for applyingwavelength conversion layers and a black (or white) matrix betweensubpixels in accordance with an embodiment. In the embodimentillustrated in FIG. 14B, the matrix 202, wavelength conversion layer310, oxygen barrier film 324, and optional color filter layer 328 areformed on the top cover 500 and pressed down over the array of micro LEDdevices 400 and light distribution layers 320. In an embodiment, the topcover 500 of FIG. 14B is a rigid glass plate, and is sealed around theperipheral edges of the display substrate 102 with a sealant. A gettermaterial may optionally be placed inside the sealed region containingthe micro LED devices and the wavelength conversion layer 310 to absorbmoisture, particularly if the wavelength conversion layer includesquantum dots. Either of the top cover configurations of FIGS. 14A-14Bcan be used when forming the display devices described and illustratedherein.

FIG. 15 is a top schematic view illustration of an array of micro LEDdevices including a variety of configurations described in FIGS. 12A-12Fin accordance with embodiments of the invention. In the particularembodiments illustrated in FIG. 15, a top electrode layer 318 is formedover a plurality of bank openings 128, and may be formed over aplurality of subpixels or pixels 106. In an embodiment, the topelectrode layer 318 is formed over all of the micro LED devices 400 inthe pixel area.

The embodiment illustrated in FIG. 12B is illustrated in the labeledpixel 106 in which the micro LED device 400 pairs are transferredwithout detection of any missing, defective, or contaminated micro LEDdevices. In this embodiment, the repair micro LED sites 401 are open,and repair micro LED devices have not been transferred.

The embodiment illustrated in FIG. 12D is also illustrated as one of thered-emitting subpixels in FIG. 15 including a repair micro LED device,where the top electrode layer 318 is formed over both the red emittingmicro LED devices 400 and the defective or contaminated micro LED device400X, where the defective or contaminated micro LED device 400X iscovered with the passivation layer 316.

Similarly, an embodiment is illustrated for one of the blue-emittingsubpixels of FIG. 15 including a repair micro LED device, where the topelectrode layer 318 is formed over both the blue emitting micro LEDdevices 400 and the bonding layer 140 corresponding to a missing microLED device.

FIG. 16 is a top schematic view illustration of an array of micro LEDdevices including a variety of configurations described in FIGS. 12A-12Fin accordance with embodiments of the invention. In the particularembodiments illustrated in FIG. 16, the arrangements of micro LEDdevices 400 are the same as those described above with regard to FIG.15. The embodiments illustrated in FIG. 16 differ from those illustratedin FIG. 15 particularly in formation of a plurality of separate topelectrode layers 318. In one embodiment, such as those illustrated inthe labeled pixel 106 where a micro LED device 400 is not placed on therepair bonding site 401, it is not required for the top electrode layers318 to be formed thereon. Accordingly, the length of the top electrodelayer 318 can be determined based upon whether or not a replacementmicro LED device is added. The top electrode layer 318 may also beformed over the bonding site 401.

In some embodiments, the top electrode layers 318 are formed by ink jetprinting or screen printing. Ink jet printing in particular may besuitable since it is a non-contact printing method. Conventional AMOLEDbackplane processing sequences typically blanket deposit the topeelectrode layer in a deposition chamber followed by singulation of theindividual backplanes from a larger substrate. In accordance withembodiments of the invention, a display substrate 102 can be singulatedfrom a larger substrate prior to transferring the array of micro LEDdevices. In an embodiment ink jet printing or screen printing provides apractical approach for patterning the individual top electrode layerswithout requiring a separate mask layer for each particularconfiguration in the redundancy and repair scheme. Line width can alsovary for the top electrode layers 118 depending upon application. Forexample, the line width may approach that of the subpixel area.Alternatively, the line width may be minimal. For example, line widthsas low as approximately 15 microns may be accomplished with commerciallyavailable ink jet printers, and line widths as low as approximately 30microns may be accomplished with commercially available screen printers.Accordingly, the line width may be more or less than the maximum widthof the micro LED devices.

FIG. 17 is a top schematic view illustration of an array of micro LEDdevices including a variety of configurations described in FIGS. 12A-12Fin accordance with embodiments of the invention. In the particularembodiments illustrated in FIG. 17, the arrangements of micro LEDdevices 400 are the same as those described above with regard to FIGS.15-16. The embodiments illustrated in FIG. 17 differ from thoseillustrated in FIG. 16 particularly in formation of the top electrodelayers 318. The embodiments illustrated in FIG. 16 were shown asaltering the length of the top electrode layers 318, while theembodiments illustrated in FIG. 17 are shown as altering the path of thetop electrode layers 318, and/or number of top electrode layers 318. Forexample, the top electrode layers 318 illustrated in FIG. 17 maycorrespond to those illustrated in FIG. 12C and FIG. 12E. In theexemplary embodiments illustrated in FIG. 17 for the red and greenemitting micro LED devices, a separate top electrode layer 318 can beformed for each micro LED device 400 in the subpixel. In the embodimentillustrated in the bottom-most blue-emitting subpixel, a single topelectrode layer 318 can be formed for multiple micro LED devices 400 ina subpixel where the path is adjusted to avoid a bonding layer 140, oralternatively a defective or contaminated micro LED device. In thismanner, adjusting the path of the top electrode layers 318 can be usedin the alternative to, or in addition to, adjusting deposition of thepassivation layer 316 to cover defective or contaminated micro LEDdevices or the bonding sites of missing micro LED devices.

The formation of separate top electrode layer(s) 318 may provide anadditional benefit during electrical testing of the display substrate102 after formation of the top electrode layer(s) 318. For example,prior to formation of the top electrode layer 318 it may not have beenpossible to detect certain defects resulting in shorting of a micro LEDdevice 400S. The implication of a shorted micro LED device 400S couldresult in a dark subpixel in which all of the current flows through theshorted micro LED devices 400S rather than any of the other micro LEDdevices in the subpixel. In the embodiment illustrated in FIG. 18 thetop electrode layer 318 connected to a shorted micro LED device 400S iscut using a suitable technique such as laser scribing. In this manner,electrical shorts that could not have been or were not detected duringthe integrated testing method previously described could potentially bedetected during an electrical test with the application of electricalcurrent through the display after formation of the top electrode layer318. In such an embodiment, if a micro LED device 400S is shorted, thetop electrode layer 318 to the micro LED device 400S can be cut,allowing the redundant and/or repair micro LED device to provide theemission from the subpixel.

FIG. 19 illustrates an alternative embodiment where rather than cuttingor scribing the top electrode layer 318, the reflective bank layer 142can be formed to include multiple bottom contact areas 124 that can becut using a suitable technique such as laser scribing to segregateirregular micro LED devices. In the particular embodiment illustrated,the bottom contact area 124 includes separate landing areas for themicro LED devices. In the particular embodiment illustrated, the bottomcontact area 124 supporting the micro LED device 400S is cut using asuitable technique such as laser scribing to segregate the irregularmicro LED device so that it is not in electrical communication with theunderlying TFT circuitry through filled opening 131.

Up until this point, embodiments of the invention have been illustratedand described with a display substrate 102 including an underlyingcircuitry 210. However, embodiments of the invention are not so limited.For example, the circuitry can be provided on top of the substrate inthe form of micro chips. FIG. 20 is a top view schematic illustration ofa smart pixel display including a redundancy and repair siteconfiguration in accordance with an embodiment of the invention. Asshown the display panel 200 includes a substrate 201 which may beopaque, transparent, rigid, or flexible. A smart pixel area 206 mayinclude separate subpixels of different emission colors, and a microcontroller chip 208 including the working circuitry described above withregard to the TFT substrate. In this manner, rather than forming thepixel area on a TFT substrate including the working circuitry, the microLED devices 400 and micro controller chip 208 are both transferred tothe same side or surface of the substrate 201. Electrical distributionlines can connect the micro controller chip 208 to the data drivercircuit 109 and scan driver circuit 112 similarly as with a TFTsubstrate. Likewise, reflective bank layer structures can be formed onthe substrate 201 similarly as described above for the TFT substrate tocontain the micro LED devices 400 and repair bonding site 401.Similarly, a top electrode layer 318, or separate top electrode layers318 can connect the micro LED devices 400 to a ground tie line 144 orground ring 116 similarly as described above with regard to the TFTsubstrate configuration. Wavelength conversion layers, and otheroptional layers, can also be formed over the micro LED devices 400 togenerate the determined color emission spectrum as described above.Thus, similar color emission configurations including wavelengthconversion layers, redundancy, and repair site configurations can beformed with the smart pixel configuration as described above for the TFTsubstrate configurations.

FIG. 21 illustrates a display system 2100 in accordance with anembodiment. The display system houses a processor 2110, data receiver2120, a display 2130, and one or more display driver ICs 2140, which maybe scan driver ICs and data driver ICs. The data receiver 2120 may beconfigured to receive data wirelessly or wired. Wireless may beimplemented in any of a number of wireless standards or protocolsincluding, but not limited to, Wi-Fi (IEEE 802.11 family), WiMAX (IEEE802.16 family), IEEE 802.20, long term evolution (LTE), Ev-DO, HSPA+,HSDPA+, HSUPA+, EDGE, GSM, GPRS, CDMA, TDMA, DECT, Bluetooth,derivatives thereof, as well as any other wireless protocols that aredesignated as 3G, 4G, 5G, and beyond. The one or more display driver ICs2140 may be physically and electrically coupled to the display 2130.

In some embodiments, the display 2130 includes one or more micro LEDdevices 400 and wavelength conversion layers 310 that are formed inaccordance with embodiments of the invention described above. Forexample, the display 2130 may include a plurality of micro LED devices,a plurality of light distribution layers around the micro LED devices,and a plurality of wavelength conversion layers over the lightdistribution layers.

Depending on its applications, the display system 2100 may include othercomponents. These other components include, but are not limited to,memory, a touch-screen controller, and a battery. In variousimplementations, the display system 2100 may be a television, tablet,phone, laptop, computer monitor, kiosk, digital camera, handheld gameconsole, media display, ebook display, or large area signage display.

In utilizing the various aspects of this invention, it would becomeapparent to one skilled in the art that combinations or variations ofthe above embodiments are possible for integrating micro LED devices andwavelength conversion layers into display applications. Although thepresent invention has been described in language specific to structuralfeatures and/or methodological acts, it is to be understood that theinvention defined in the appended claims is not necessarily limited tothe specific features or acts described. The specific features and actsdisclosed are instead to be understood as particularly gracefulimplementations of the claimed invention useful for illustrating thepresent invention.

What is claimed is:
 1. A display panel comprising: a display substrateincluding an array of pixels; a first pixel of the array of pixels thatincludes a first subpixel designed for a first color emission spectrum,and a second subpixel designed for a second color emission spectrumdifferent from the first color emission spectrum; a first vertical lightemitting diode (LED) mounted on a first bottom electrode within thefirst subpixel; a second vertical LED mounted on a second bottomelectrode within the second subpixel; a sidewall passivation materialthat laterally surrounds the first and second vertical LEDs; a topelectrode layer that spans over the sidewall passivation layer materialand the first and second vertical LEDs, and is in electrical contactwith the first and second vertical LEDs; a first wavelength conversionlayer comprising phosphor particles over the top electrode layer and thefirst vertical LED, wherein the first wavelength conversion layer is notover the second vertical LED.
 2. The display panel of claim 1, whereinthe display substrate further comprises a terminal line, and the topelectrode layer electrically connects the first vertical LED and thesecond vertical LED to the terminal line.
 3. The display panel of claim2, wherein the first and second vertical LEDs each have a maximum widthof 1-100 um.
 4. The display panel of claim 2, wherein the first verticalLED is mounted to the first bottom electrode within a bank opening. 5.The display panel of claim 4, wherein the first wavelength conversionlayer completely covers the bank opening.
 6. The display panel of claim4, further comprising a reflective bank layer within the bank opening.7. The display panel of claim 6, wherein the first wavelength conversionlayer completely covers the bank opening.
 8. The display panel of claim6, wherein the reflective bank layer is the first bottom electrode. 9.The display panel of claim 4, wherein the second vertical LED is mountedto the second bottom electrode within a second bank opening.
 10. Thedisplay panel of claim 9, further comprising a second reflective banklayer within the second bank opening.
 11. The display panel of claim 2,further comprising a black matrix layer arranged between the first andsecond subpixels.
 12. The display panel of claim 2, wherein the phosphorparticles are quantum dots.
 13. The display panel of claim 12, whereinthe first wavelength conversion layer further comprises scatteringparticles.
 14. The display panel of claim 1, further comprising a colorfilter over the first wavelength conversion layer, wherein the colorfilter is designed to filter out light emitted from the first verticalLED.
 15. The display panel of claim 1, further comprising an array ofcontroller chips in a pixel areas of the display substrate, eachcontroller chip to switch and drive a corresponding plurality ofvertical LEDs.
 16. The display panel of claim 15, wherein the array ofcontroller chips includes a first controller chip to switch and drivethe first and second vertical LEDs.
 17. The display panel of claim 1,wherein the first and second vertical LEDs are bonded to the first andsecond bottom electrodes with a solder material.
 18. The display panelof claim 17, wherein each of the first and second vertical LEDscomprises a p-n diode, and a conformal dielectric barrier layer spanningsidewalls of the p-n diode.